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COLUMBIA    UN1VERSLTY 
DEPARTMENT     OF     PHYSIOLOGY 
THE    JOHN    G.   CURTIS    LIBRARY 


MANUALS 

FOR 

Students   of   Medicine. 


ELEMENTS 


OF 


HISTOLOGY. 


BY 


E.  KLEIN,  M.  D.,  P.  R.  8., 

.JOINT-LECTURER  ON   GENERAL  ANATOMY  AND  PHYSIOLOGY   IM   THE 

MEDICAL  SCHOOL  OP  ST.  BARTHOLOMEW'S  HOSPITAL, 

LONDON. 


ILLUSTRATED  WITH  181  ENGRAVINGS. 


PHILADELPHIA: 
HENRY   C.  LEA'S  SON  &  GO. 

1883. 


' 


-v  e:  c 


To 
WILLIAM  BOWMAN,  LL.  D.,  F.  K.  S.,  &c,  &c, 

THIS  BOOK  IS  DEDICATED, 

IN    ACKNOWLEDGMENT     OF    HIS     MANY    AND     GREAT    DISCOVERIES 

IN  ANATOMY  AND    PHYSIOLOGY. 


STANDARD  WORKS  ON 
PATHOLOGY   AND   HISTOLOGY. 


A    MANUAL    OF   PATHOLOGICAL    HIS- 

tology.  By  V.  Cornil,  Professor  in  the  Faculty  of 
Medicine  of  Paris,  and  L.  Ranvier,  Professor  in  the 
College  of  France.  Translated  with  Notes  and  Addi- 
tions, by  E.  O.  Shakespeare,  M.  D.,  Pathologist  to  the 
Philadelphia  Hospital,  and  J.  Henry  C.  Simes,  M.  D., 
Demonstrator  of  Pathological  Histology  in  the  Uni- 
versity of  Pennsylvania.  Octavo,  800  pages,  360  illus- 
trations.   Cloth,  $5.50;  leather,  $6.50;  half  Russia,  $7. 

PATHOLOGY  AND  MORBID  ANATOMY. 

By  T.  Henry  Green,  M.  D.,  Lecturer  on  Pathology 
and  Morbid  Anatomy  at  Charing  Cross  Hospital  Medical 
School,  London.  Fifth  American  from  the  sixth  en- 
larged and  revised  English  edition.    Preparing. 


A    TREATISE    ON  PATHOLOGY.     By 

Joseph  Coats,  M.  D.,  F.  F.  P.  S.,  Pathologist  to  the 
Glasgow  Western  Infirmary.  Octavo,  about  900  pages, 
339  illustrations.    Shortly. 


SPECIAL   ANATOMY  AND  HISTOLOGY. 

By  William  E.  Horner,  M.  D.,  Professor  of  Anatomy, 
University  of  Pennsylvania.  Eighth  edition.  Two 
octavo  volumes,  1007  pages,  320  illustrations.    Cloth,  $6. 


ATLAS  OF  PATHOLOGICAL  HISTOLOGY. 

By  Dr.  Gottlieb  Gluge.  Translated  by  Joseph 
Leidy,  M.D.  Quarto,  96  pages  of  letter-press,  with 
320  plain  and  colored  figures  on  copper-plates.  Cloth,  $4. 


HENRY  C.  LEA'S  SON  &  CO.,  PHILADELPHIA. 


PREFACE. 


This  Work  is  intended  as   a   Manual    for    Medical 

Students.      The  original  plan  was  to  embody  in  it 

only  such  matter  as  was  absolutely  required  for  the 

first  year's  student  in  the  Medical  Schools ;  but  this 

plan  was  not  carried  out,  since  the  book  would  then 

have  been,  in  some  measure,  incomplete  as  a  Manual 

of  Histology.     The  work  contains  a  good  deal  that 

will  be   acceptable  to  the  advanced  student,  as  well 

as  to  the  beginner. 

My  best  thanks  are  due  to  Mr.  Charles  Berjeau, 

F.L.S.,  for  the  readiness  and  artistic  skill  with  which 

lie  has  executed  the  illustrations  on  wood.     Some  of 

the  figures  are  copied  from  the  "Atlas  of  Histology," 

others  from  the  "  Handbook    for    the   Physiological 

Laboratory."     The  former  are  marked   "  Atlas,"  the 

latter  "Handbook." 

E.  KLEIN. 

May,  1883. 


CONTENTS. 


CHAPTER  I.                                        page 
Cells 1 

CHAPTER   II. 
Blood 10 

CHAPTER   HI. 
Epithelium 16 

CHAPTER  IV. 
Endothelium 25 

CHAPTER   V. 
Fibrous  Connective  Tissues 31 

CHAPTER   VI. 
Cartilage 45 

CHAPTER   VII. 
Bone 53 

CHAPTER   VIII. 
Non-striped  Muscular  Tissue 63 

CHAPTER   IX. 

Striped  Muscular  Tissue 66 

CHAPTER   X. 
The  Heart  and  Blood-vessels 74 

CHAPTER    XI. 

The  Lymphatic  Vessels 84 


x  Elements  of  Histology. 

CHAPTER   XII.                                     page 
Simple  Lymphatic  Glands 92 

CHAPTER   XIII. 
Compound  Lymphatic  Glands 98 

CHAPTER   XIV. 
Nerve-fibres .       .       .       .103 

CHAPTER    XT. 
Peripheral  Nerve-endings  ' 115 

CHAPTER   XVI. 
The  Spinal  Cord 127 

CHAPTER    XVII. 
The  Medulla  Oblongata 142 

CHAPTER   XVIII. 
The  Cerebrum  and  Cerebellum 149 

CHAPTER   XIX. 
The  Cerebro-spinal  Ganglia 163 

CHAPTER   XX. 
The  Sympathetic  System 166 

CHAPTER   XXI. 
Teeth 171 

CHAPTER   XXII. 
The  Salivary  Glands 178 

CHAPTER   XXIII. 
The  Mouth,  Pharynx,  and  Tongue 1S7 

CHAPTER   XXIV. 
The  (Esophagus  and  Stomach 194 

CHAPTER   XXV. 
The  Small  and  Large  Intestine 201 


Contents.  xi 

CHAPTER   XXVI.  page 

The  Glands  of  Brunner,  and  the  Pancreas      .       .       .208 

CHAPTER   XXVII. 
The  Liver 210 

CHAPTER   XXVIII. 
The  Organs  of  Respiration 215 

CHAPTER   XXIX. 
The  Spleen 225 

CHAPTER   XXX. 
The  Kidney,  Ureter,  and  Bladder 229 

CHAPTER   XXXI. 

The  Male  Genital  Organs 244 

CHAPTER   XXXH. 
The  Female  Genital  Organs 257 

CHAPTER   XXXIII. 
The  Mammary  Gland 270 

CHAPTER   XXXIV. 
The  Skin 274 

CHAPTER   XXXV. 
The  Conjunctiva  and  its  Glands 291 

CHAPTER    XXXVI. 

The  Cornea,  Sclerotic,   Ligamentum  Pectinatum,  and 

Ciliary  Muscle 295 

CHAPTER    XXX VH. 
The  Iris,  Ciliary  Processes,  and  Choroidea       .       .       .300 

CHAPTER   XXXVIII. 
The  Lens  and  Vitreous  Body 305 

CHAPTER   XXXIX. 
The  Retina 30S 


xii  Elements  of  Histology. 

CHAPTER   XL.                                     page 
The  Outer  and  Middle  Ear 318 

CHAPTER   XLI. 
The  Internal  Ear 320 

CHAPTER   XLII. 

The  Nasal  Mucous  Membrane 333 

CHAPTER  XLIII. 
The  Ductless  Glands 338 

Index .  343 


Elements  of  Histology. 


CHAPTER    I. 

CELLS. 

1.  The  ripe  ovum  (Fig.  1)  of  man  and  mammals  is 
a  minute  spherical  clump  of  a  soft,  gelatinous,  trans- 
parent, granular-looking  substance,  containing  nume- 
rous minute  particles — yolk 
globules.  It  is  invested 
by  a  vertically-striated  deli- 
cate membrane,  called  the 
zona  pellucida.  Inside  this 
clump,  and  situated  more 
or  less  excentrically,  is  a 
vesicle — the  germinal  vesicle 
— and  inside  this,  one  or  more 
solid  spots  —  the  germinal 
spot  or  spots.  The  gela- 
tinous transparent  substance 
of  the  ovum,  containing  a 
very  large  percentage  of  proteid  material,  is  called 
Protoplasm.  Before  and  immediately  after  fertilisa- 
tion, the  protoplasm  of  the  ovum  shows  distinct  move- 
ment, consisting  in  contraction  and  expansion.  These 
movements  are  spontaneous — i.e.,  not  caused  by  any 
directly  visible  external  influence. 

The  diameter  of  the  ripe  ovum  in  man  and  domestic 
animals  varies  between  ^i-Q  and  i~ko  °^  an  incn-  But 
before  it  ripens  the  ovum  is  considerably  smaller — in 

B 


io^iim—c 


Fig.  1. — Bipe  Ovum  of  Cat. 

a,  Zona  pellucida ;  6,  germinal 
vesicle;  c,  protoplasm. 


Elements  of  Histology. 


[Chap.  i. 


fact,  its  size  is  in  proportion  to  its  state  of  develop- 
ment. 

2.  Fertilisation  causes  marked  changes  in  the 
contractions  of   the  protoplasm  of  the  ovum ;  these 


""**■  *'^i*&fcsfyi£& 


Fig.  2. — From  a  Section  through  the  Blastoderm  of  Chick,"  unincubated. 

a,  Cells  forming  the  ectoderm  ;  b,  cells  forming  the  endoderm  ;  c,  large 

formative  cells ;  /,  segmentation  cavity.    (Handbook.) 

lead  to  cleavage  or  division  of  its  body  into  two  parts, 
the  germinal  vesicle  having  previously  split  up  into 
two  bodies  or  nuclei ;  so  that  we  now  find  the  ovum 


Fig.  3a.— From  a  Section  through  the  Rudiment  of  the  Embryo  Chick. 

e,  Primitive  groove  ;  /,  dorsal  laminae  of  epiblast ;  d,  mesoblast.    The 
thin  layer  of  spindle-shaped  cells  is  the  hypoblast.    (Handbook.) 

has  originated  two  new  elements,  each  of  which  con- 
sists of  protoplasm,  of  the  same  substance  as  that  of 
the  original  ovum,  and  each  contains  one  nucleus  or 
kernel.     The  investment  of  the  ovum  takes  no  part  in 


Chap.  I.] 


Cells. 


this  process  of  division.     Not  long  after,  each  of  the 
two  daughter  elements  undergoes  cleavage  or  division 


Fig.  3b. — Vertical  Section  through  the  Ovum  of  Buf  o  Cinereus,  in  the 

early  stage  of  the  Emhryo  Development. 
a,  Tegmental  layer  of  epiblast ;  6,  dorsal  groove ;  c,  rudiment  of  central  nervous 

system  ;  d,  notochord ;  e,  deep  layer  of  epiblast ;  /,  mesoblast ;  g,  hypoblast ; 

h,  cavity  of  alimentary  canal— Rusconi's  cavity ;  h,  central  yolk ;  k,  remainder 

of  von  baer's  or  segmentation  cavity.    (Handbook.) 


into  two  new  elements,  the  nucleus  having  previously 
divided  into  two,  so  that  each  of  the  new  offspring 
possesses  its  own  nucleus.  This  process  of  division  is 
continued  in  the  same  manner  for  many  generations 


4  Elements  of  Histology.  [Chap,  i 

(Figs.  2,  3a,  3b),  so  that  after  a  few  days  we  find 
within  the  original  investment  of  the  ovum  a  large 
number  of  minute  elements,  each  consisting  of 
protoplasm,  and  each  containing  a  nucleus. 

3.  From  these  elements,  which  become  smaller  as 
the  process  of  cleavage  progresses,  all  parts  and  organs 
of  the  embryo  and  its  membranes  are  formed.  It  can 
be  easily  shown  that  the  individual  elements  possess 
the  power  of  contractility.  Either  spontaneously  or 
under  the  influence  of  moderate  heat,  electricity, 
mechanical  or  chemical  stimulation,  they  throw  out 
processes  and  withdraw  them  again,  their  substance 
flowing  slowly  but  perceptibly  along.  Hence  they 
can  change  their  position.  In  this  respect  they  com- 
pletely resemble  those  lowest  organisms  which  are 
known  as  amoebae,  each  of  these  being  likewise  a 
nucleated  mass  of  protoplasm.  Wherefore  this  move- 
ment is  termed  amoeboid  movement.  It  can  be  further 
shown  that  they,  like  amoebae,  grow  in  size  and  divide 
— that  is  to  say,  the  individuals  of  a  generation  grow 
in  size  before  each  gives  rise  to  two  new  daughter 
individuals. 

4.  Although  for  some  time  during  embryonal  life 
the  elements  constituting  the  organs  of  the  embryo  are 
possessed  of  these  characters,  a  time  arrives  when 
only  a  limited  number  of  them  retain  the  power  of 
contractility  in  any  marked  degree.  At  birth  only  the 
white  corpuscles  of  the  blood  and  lymph,  many  of  the 
elements  of  the  lymphatic  organs,  and  the  muscular 
tissues,  possess  this  power,  while  the  others  lose  it, 
or  at  any  rate  do  not  show  it  except  when  dividing 
into  two  new  elements.  Some  of  these  elements 
retain  their  protoplasmic  basis  ;  as  a  rule,  each  con- 
tains one  nucleus  (but  some  two  or  more)  and  is 
capable  of  giving  origin  by  division  to  a  new  genera- 
tion. Others,  however,  change  their  nature  altogether, 
their    protoplasm    and    nucleus   disappear,   and   they 


chap,  i.]  Cells.  5 

give  origin  to  material  other  than  protoplasm — e.g., 
collagenous,  osseous,  elastic,  and  other  substances. 

5.  Beginning  with  the  ovum,  and  ending  with  the 
protoplasmic  nucleated  elements  found  in  the  organs 
and  tissues  of  the  embryo  and  adult,  we  have,  then, 
one  uninterrupted  series  of  generations  of  elements, 
which  with  Schwann  we  call  cells  and  with  Briicke 
elementary  organisms.  Of  these  it  can  be  said  that 
not  only  is  each  of  them  derived  from  a  cell  ( Yirchow  : 
omnis  cellula  a  cellula),  but  each  consists  of  the 
protoplasm  of  Max  Schultze   (Sarcode  of  Dujardin), 


Fig.  4. — Amoeboid  movement  of  a  White  Blood  Corpuscle  of  Man ; 
various  phases  of  movement.    (Handbook.) 

is  without  any  investing  membrane,  and  includes 
generally  one  nucleus,  but  may  contain  two  or  more. 
We  can  further  say  that  each  of  these  cells  shows  the 
phenomenon  of  growth,  which  presupposes  nutrition, 
and  reproduction.  All  of  them  in  an  early  stage  of 
their  life  history ,  and  some  of  them  throughout  it, 
show  the  phenomenon  of  contractility,  or  amoeboid 
movement  (Fig.  4.) 

Cells  differ  in  shape  according  to  kind,  locality, 
and  function,  being  spherical,  irregular,  polygonal, 
squamous,  branched,  spindle-shaped,  cylindrical,  pris- 
matic, or  conical.  These  various  shapes  will  be  more 
fully  described  when  dealing  in  detail  with  the  various 
kinds  of  cells.  Cells  in  man  and  mammals  differ  in 
size  within  considerable  limits  :  from  the  size  of  a 
small  white  blood  corpuscle  of  about  a-5100  of  an  inch 
to  that  of  a  large  ganglion  cell  in  the  anterior  horns  of 
the  spinal  cord  of  about  ^-L  of  an  inch,  or  to  that  of  a 


6  Elements  of  Histology.  [Chap.  i. 

multinucleated  cell  of  the  bone  marrow — myeloplax — 
some  of  which  surpass  in  size  even  the  ganglion  cells. 
The  same  holds  good  of  the  nucleus.  Between  the 
nucleus  of  a  ganglion  cell  of  about  -—-$  to  ygVo  °^  an 
inch  in  diameter  and  the  nucleus  of  a  white  blood 
corpuscle  of  about  5q00  to  -,  0q00  of  an  inch  and  less 
there  are  all  intermediate  sizes. 

6.  Protoplasm  is  a  transparent  homogeneous  or 
granular-looking  substance.  On  very  careful  examina- 
tion with  good  and  high  powers,  and  especially  when 
examined  with  certain  reagents,  in  many  instances  it 
shows  a  more  or  less  definite  structure,  composed  of 
fibrils,  more  or  less  regular,  and  in  some  instances 
grouped  into  a  honeycombed  or  fibrillar  reticulum 
in  the  meshes  of  which  is  a  homogeneous  interstitial 
substance.  The  closer  the  meshes  of  the  reticulum, 
the  less  there  is  of  this  interstitial  substance,  and  the 
more  regularly  granular  does  it  appear.  In  the  meshes 
of  the  reticulum,  however,  may  be  included  larger  or 
smaller  granules  of  fat,  pigment,  or  other  material. 
Water  makes  protoplasm  swell  up,  and  ultimately 
become  disintegrated ;  so  do  dilute  acids  and  alkalies. 
All  substances  that  coagulate  proteids  have  the  same 
effect  on  protoplasm. 

7.  The  nucleus,  the  size  of  which  is  generally  in 
proportion  to  that  of  the  cell,  is  usually  spherical  or 
oval.  It  is  composed  of  a  more  or  less  distinct  invest- 
ing cuticle  and  the  nuclear  contents,  which  are  in  the 
ripe  state  arranged  as  an  irregular  or  regular  network, 
the  parts  of  which  may  be  uniform  fibrils  or  septa,  or 
irregularly-shaped  trabecule.  In  the  life  history  of 
each  nucleus  there  may  be  stages  in  which  one  or  more 
clumps  or  nucleoli  are  present  in  the  nuclear  network. 
The  substance  of  the  nucleus  differs  chemically  from 
that  of  the  cell,  the  former  containing  nuclein. 

Immediately  before  division  the  nuclear  membrane 
disappears,  and  also  immediately  after   division  the 


Chap,  i.]  Cells.  7 

nuclear  matter  shows  no  definite  boundary.  The 
nuclear  membrane  when  present  is  a  condensed  outer 
stratum  of  the  nuclear  matter. 

In  some  instances  it  can  be  shown  that  the 
nuclear  fibrils  are  in  continuity  with  the  fibrils  of  the 
cell  substance.  In  the  moving  white  blood  corpuscles 
Strieker  and  Unger  have  seen  the  nucleus  becoming 
one  with  the  cell  substance,  and  again  afterwards 
differentiated  by  the  appearance  of  a  membrane. 

8.  During  division  of  the  cell  the  nucleus 
divides  generally  before  the  cell  protoplasm.  This 
division  of  the  nucleus  has  previously  been  supposed 
to  occur  in  the  same  manner  as  that  of  the  cell  pro- 
toplasm— i.e.,  by  simple  cleavage.  This  mode  is  called 
the  direct  division,  or  Remak's  mode  of  division. 
In  this  division  the  nucleus  is  supposed  to  become 
constricted,  kidney-shaped  and  hour-glass  shaped,  and 
if  the  division  is  into  more  than  two,  lobed.  Nuclei 
of  these  shapes  are  not  uncommon ;  but  they  need  not 
necessarily  indicate  direct  division,  because,  being 
very  soft  structures,  pressure  exerted  from  outside,  or 
the  motion  of  the  cell  protoplasm,  may  produce  these 
shapes ;  and,  further,  the  contractility  of  the  nucleus 
may  and  occasionally  has  been  observed  to  cause 
these  changes  of  shape.  From  the  observations  of 
recent  investigators — Butschli,  Hertwig,  Strassburger, 
Mayzel,  van  Beneden,  Balfour,  Eberth,  Schleicher, 
Peremeschko,  Flemming,  Klein,  Arnold,  Pfutzner, 
Retzius,  Bizzozero,  and  many  others — it  is  now  known 
that  in  the  embryo  and  adult,  in  plant  and  animal, 
vertebrates  and  invertebrates,  all  kinds  of  cells,  before 
their  protoplasm  undergoes  division,  show  complicated 
changes  of  their  nucleus,  leading  to  division.  This 
manner  of  division  is  called  the  indirect  division  or 
karyokinesis.  It  has  been  observed  by  Mayzel, 
Schleicher,  and  Flemming,  that  the  nuclear  fibrils 
show  movement,  hence  the  name  karyokinesis.     This 


8 


Elements  of  Histology. 


[Chap.  I. 


process  of  the  karyokinesis  is  represented  in  the  ad- 
joining figure,  5,  and  it  consists  of  the  following  phases : 
(a)  The  nuclear  network  become  very  pronounced, 
while  the  nuclear  membrane  disappears,  and  the 
fibrils  of  the  nuclear  network  becomes  twisted  and 
bent  into  a  more  or  less  dense  convolution;  at  the 
same  time  the  nucleus,  as  a  whole,  is  considerably 
enlarged,      (b)  The  fibrils  unravel  into  loops,  arranged 


G  H 

Fig.  5. — Karyokinesis. 

a,  Ordinary  nucleus  of  a  columnar  epithelial  cell ;  b,  c,  the  same  nucleus  in  the 
stage  of  convolution ;  r>,  the  wreath,  or  rosette  form  ;  k,  the  aster,  or  single 
star ;  f,  a  nuclear  spindle  from  the  Descemet's  endothelium  of  the  frog's 
cornea;  6,  h,  i,  diaster ;  k,  two  daughter  nuclei. 

around  the  centre  as  a  wreath  or  rosette,  (c)  The 
peripheral  points  of  the  loops  become  broken,  and 
we  obtain  a  star-shaped  figure  of  single  loops — the 
aster,  (d)  The  loops  separate  into  two  groups  or 
new  centres :  this  is  the  diaster,  or  double  star, 
(e)  The  two  groups  of  threads  become  further  apart, 
as  if  attracted  by  opposite  poles;  but  the  two  groups 
remain  still  connected  with  one  another  by  fine  pale 
threads.  These  latter  differ  from  the  others  in  not 
staining  with  certain  dyes,  and  representing  the  in- 


chap,  i.]  Cells.  g 

terstitial  substance  of  the  nuclear  matter — i.e.,  the  pale 
substance  contained  in  the  original  reticulum  of  the 
nucleus.  Flemming  calls  this  substance  achromatin, 
whereas  the  threads  forming  the  original  network,  the 
convolution,  aster  and  diaster,  he  calls  chromatin,  on 
account  of  its  readily  staining  with  dyes. 

In  this  stage  the  whole  figure  resembles  a  spindle, 
the  nuclear  spindle  of  Biitschli  (Fig.  5,  f). 

(/)  Further,  all  connection  between  the  two  sets 
of  threads  is  broken — i.e.,  between  the  stars  of  the 
diaster.  (g)  The  threads  of  each  set  become  greatly 
convoluted.  (A)  A  membrane  appears  for  each  set. 
In  this  stage  we  speak  of  two  new  or  daughter  nuclei. 
The  cell  protoplasm  may  commence  to  divide  at  any 
stage  between  the  one  when  the  threads  aggregate 
round  two  centres,  and  the  one  when  two  distinct 
daughter  nuclei  are  present ;  or  the  division  of  the 
nucleus  may  not  be  followed  by  the  division  of  the  cell 
protoplasm,  in  which  case  we  have  a  two-nucleated 
cell.  In  some  instances,  especially  of  invertebrates  and 
lower  vertebrates,  a  peculiar  sun-like  arrangement  of 
fibrils  of  the  cell  protoplasm  towards  each  of  the  two 
stars  of  the  above  nuclear  fibrils  has  been  observed. 
Martin  has  noticed,  in  pathological  new  growths,  a 
simultaneous  division  into  three  and  four  daughter 
nuclei,  after  the  mode  of  karyokinesis.  Although 
this  indirect  mode  of  division  of  the  nucleus  has  been 
observed  in  all  kinds  of  cells  in  the  embryo,  and  to  a 
limited  degree  also  in  the  adult,  it  is  not  proved  to 
be  the  universal  mode  of  nuclear  division.  On  the 
contrary,  there  is  strong  evidence  that  in  amoeboid 
corpuscles  division  of  the  nucleus  follows  the  direct 
mode,  and  it  is  also  probable  that  other  nuclei,  under 
certain  conditions,  may  undergo  the  direct  mode  of 
division. 


IO  [Chap.  II. 


CHAPTER   II. 

BLOOD. 

9.  Under  the  microscope  blood  appears  as  a  trans- 
parent fluid,  the  liquor  sanguinis  or  plasma,  in  which 
float  vast  numbers  of  formed  bodies,  the  blood  cor- 
puscles. The  great  majority  of  these  are  coloured: 
a  few  of  them  are  colourless.  The  latter  are  called 
vihite  or  colourless  blood  corpuscles,  or  leucocytes. 
The  former  are  called  red  or  coloured  blood  corpuscles, 
and  appear  red  only  when  seen  in  a  thick  layer; 
when  in  a  single  layer  they  appear  of  a  yellow- 
greenish  colour,  more  yellow  if  of  arterial,  more 
green  if  of  venous  blood.  The  proportions  of 
plasma  and  blood  corpuscles  are  sixty-four  of  the 
former  and  thirty-six  of  the  latter  in  one  hundred 
volumes  of  blood.  By  measurement  it  has  been  found 
that  there  are  a  little  over  five  millions  of  blood 
corpuscles  in  each  cubic  millimetre  (-^-g  of  a  cubic  inch) 
of  human  blood.  There  appears  to  be  in  healthy 
human  blood  one  white  corpuscle  for  600-1200  red 
ones.  In  man  and  mammals  the  relative  number  of 
blood  corpuscles  is  greater  than  in  birds,  and  in  birds 
greater  than  in  lower  vertebrates. 

10.  The  red  blood  corpuscles  (Fig.  6)  of  man 
and  mammals  are  homogeneous  bi-concave  discs  (except 
in  the  camelidse,  where  they  are  elliptical),  and  do  not 
possess  any  nucleus.  Being  bi-concave  in  shape,  they 
are  thinner  and  more  transparent  in  the  centre  than 
at  the  periphery.  In  other  vertebrates  they  are  oval 
and  more  or  less  flattened  from  side  to  side,  and  each 
possesses  a  central  oval  nucleus. 

The  diameter  of  the  human  red  blood  corpuscles  is 


Chap.  II.] 


Blood. 


ii 


about  -g^j-o  of  an  inch  on  the  broad,  and  T^Joo"  °^  an 

inch   on   the   narrow    side.      But   there   are    always 

corpuscles  present  which  are  much  smaller  by  about 

one-third    to   one-half 

than  the  others.       In 

normal      blood     these 

small    red    corpuscles 

are  scarce ;  in  certain 

abnormal      conditions, 

especially   anemia,   or 

scarcity  of  blood,  they 

are     more    numerous. 

According  to  Gulliver,  Welcker,  and  others,  the 
following  are  the  measurements  of  the  sizes  of  red 
blood  corpuscles  of  various  vertebrates  : — man, 


A  B  ^^  C 

Fig.  6.— Various  kinds   of  Eed  Blood 
Corpuscles. 

A,  Two  human,  one  seen  from  the  broad, 
the  other  from  the  narrow  side ;  b,  a  red 
corpuscle  of  the  camel ;  c,  two  red  corpus- 
cles of  the  frog,  one  seen  from  the  broad, 
the  other  from  the  narrow  side. 


elephant, 


3200  > 

i . 

2745   J 


5000  y 
;  pigeon,  ^ftt  >  toad> 


d°g>  mnro  J  cat>  Toko  \  sneeP> 

horse,  ^Vo  \  musk  deer>  T2W5 

rcnnr  J  newt>  irhr  l  proteus,  ^ ;  pike,  -^Vo  y  shark> 
1 

1142" 

11.  In  a  microscopic  specimen  of  fresh  unaltered  blood 
(Fig.  7)  the  red  blood  corpuscles  form  peculiar  shorter 

or  longer  rolls,  like  so 
many  coins,  becoming 
adherent  to  one  another 
by  their  broad  surfaces. 
Under  various  condi- 
tions— such  as  when 
isolated,  or  when  blood 
is  diluted  with  saline 
solution  or  solutions  of 
other  salts  (sulphate  of 
sodium  or  magnesium) 
— the  corpuscles  lose 
their  smooth  circular 
outline,  shrinking  and 
In  a  further  stage  of  this 
process  of  shrinking  they  lose  their  discoid  form,  and 


Fig.  7.— Human  Blood,  fresh.. 

A,  Rouleaux  of  red  corpuscles ;  b,  isolated 
red  corpuscle  seen  in  profile  ;  c,  isolated 
red  corpuscle  seen  from  its  broad  sur- 
face ;  d,  white  corpuscles. 


becoming  crenate  (Fig.  8,  a). 


12 


Elements  of  Histology. 


[Chap.  II. 


become  smaller  and  spherical,  but  beset  all  over  their 

surface  with  minute  processes.    This  shape  is  called  the 

horse-chestnut  shape  (Fig.  8,  b,  c).    It  is  pro- 

f%  f%        bably  due  to  the  corpuscles  losing  carbonic 

acid,  as  its  addition  brings  back  their  discoid 

shape  and  smooth  circular  outline.     On  ab- 

w      w      stracting  the  carbonic  acid  they  return  to 

the    horse-chestnut    shape.     Water,    acid, 

alcohol,  ether,    the    electric    current,  and 

many  other  reagents,  produce  discoloration 

of  the  red  blood  corpuscles ;  the  colouring 

matter  —  generally    the    combination     of 

the  blood -colouring   matter  with   globulin  known    as 

Jicemoglobin — becoming     dissolved     in     the     plasma. 

What    is     left    of     the     corpuscles    is     called    the 

stroma.     In  newts'  and  frogs'  blood  a  separation  of 

the    stroma      from     the 


Fig.  8.— Human 
Red  Blood 
Corpuscles. 

a,  Creiiate  ;  5,  c, 
horse-chestnut 
shaped. 


o  a 


o, 


Fig. 


O 


9.— Eed  Blood  Corpuscles 
Man  and  Newt. 


nucleus  plus  haemoglobin 
can  be  effected  by  means 
of  boracic  acid  (Fig.  9,  b)  ; 
the  former  is  called  by 
Briicke  the  Oikoid,  the 
latter  Zooid.  This  stroma 
contains  amongst  other 
things  a  good  deal  of  para- 
globulin.  The  stroma 
of  the  corpuscles  of 
amphibians  is  seen, 
under  certain  reagents, 
to    be    of    a    reticulated 

structure,  but  in  the  fresh  state  appears  homo- 
geneous and  pale.  Discoloration  of  the  blood  cor- 
puscles can  be  observed  to  take  place  also  in  blood 
without  the  addition  of  any  or  with  that  of  per- 
fectly harmless  fluids,  such  as  humor  aqueus  of 
the  eye,  hydrocele  fluid,  &c.  The  number  of  cor- 
puscles undergoing  discoloration  is,  however,  small. 


A,  Human  red  corpuscles  after  the  action 
of  tannic  acid :  a,  three  red  corpuscles, 
from  which  the  haemoglobin  is  passing 
out ;  6,  Roberts's  corpuscles. 

B,  Newt's  red  corpuscles  after  the  action 
of  boracic  acid :  a,  a  corpuscle  showing 
Brtickes'  zooid  and  oikoid ;  6,  a  corpus- 
cle showing  the  reticulated  stroma; 
c,  a  corpuscle  showing  the  reticulum 
in  the  nucleus ;  d,  the  nucleus  passing 
out. 


Chap.  II.] 


Blood. 


!3 


The  elements  of  the  blood  described  by  Dr.  William 
Norris,  of  Birmingham,  as  the  invisible,  pale,  or  third 
corpuscle,  are  simply  red  blood  corpuscles  that  have 
become  discoloured  by  the  mode  of  preparation 
(Alice  Hart). 

12.  The  haemoglobin  of  the  red  blood  corpuscles 
forms  crystals  (Fig.  10),  which  differ  in  shape  in  the 
various    mammals. 

They  are  always 
of  microscopic  size, 
and  of  a  bright  red 
colour. 

In  man  and 
most  mammals 
they  are  of  the 
shape  of  prismatic 
needles,  or  rhombic 
plates ;  in  the 
squirrel  they  are 
hexagonal  plates, 
and  in  the  guinea-pig  they  are  tetrahedral  or  octa- 
hedral. The  blood  pigment  itself  is  an  amorphous 
dark-brown  or  black  powder — the  hcematin  ;  but  it 
can  be  obtained  in  a  crystalline  form  as  hydro- 
chlorate  of  h8ematin(Fig.  11).  These  crystals 
^^jjkfe  also  are  of  microscopic  size,  of  a  nut-brown 
*g»  4  colour,  of  the  shape  of  narrow  rhombic 
"  "  plates,  and  are  called  hcemin  crystals,  or 
Teichmann's  crystals.  In  extravasated 
human  blood  crystals  of  a  bright  yellow 
or  orange  colour  are  occasionally  met  with  ;  they  are 
called  by  Virchow,  their  discoverer,  hcematoidin. 
They  are  supposed  to  be  identical  with  bilirubin, 
obtainable  from  human  bile. 

13.  The  white  or  colourless  blood  cor- 
puscles are  in  human  blood  of  about  ^ oVo  *°  2W0 
of  an   inch    in   diameter,    and    are    spherical   in   the 


Fig.  10. — Haemoglobin  crystals. 
A,  Of  guinea-pig ;  b,  of  squirrel ;  c,  d,  human. 


Fig.U.— Hse- 
min  crystals. 


i'4  Elements  of  Histology.         [chap.  n. 

circulating  blood  or  in  blood  that  has  just  been 
removed  from  the  vessels.  Their  substance  is  trans- 
parent granular-looking  protoplasm,  containing  larger 
or  smaller  bright  granules.  These  granules  are 
either  of  a  fatty  nature,  or,  as  in  some  kinds  of 
blood,  notably  horses',  are  of  a  reddish  colour, 
and  these  corpuscles  are  supposed  by  some  observers 
(Semmer  and  Alexander  Schmidt)  to  be  inter- 
mediate between  red  and  white  corpuscles.  The 
protoplasm  of  the  colourless  corpuscles  contains 
glycogen  (Ranvier,  Sch'afer).  In  the  blood  of  lower 
vertebrates  the  colourless  corpuscles  are  considerably 
larger  than  in  mammals.  But  in  all  cases  they 
consist  of  protoplasm,  include  one,  two,  or  more 
nuclei,  and  show  amoeboid  movement.  This  may  be 
observed  in  corpuscles  without  any  addition  to  a 
fresh  microscopic  specimen  of  blood,  but  it  always 
becomes  much  more  pronounced  on  applying  artificial 
heat  of  about  the  degree  of  mammals'  blood.  It 
is  then  seen  that  they  throw  out  longer  or  shorter 
filamentous  processes,  which  may  gradually  lengthen 
or  be  withdrawn,  appearing  again  at  another  point  of 
the  periphery.  The  corpuscle  changes  its  position 
either  by  a  flowing  movement  of  its  protoplasm  as  a 
whole,  thus  rapidly  creeping  along  the  field  of  the 
microscope,  or  it  may  push  out  a  filamentous  process 
and  shift  the  rest  of  its  body  into  it.  During  this 
movement  the  corpuscle  may  take  up  granules  from 
the  surrounding  fluid. 

14.  The  white  corpuscles  of  the  same  sample  of 
blood  differ  in  size  and  aspect  within  considerable 
limits,  some  being  half  the  size  of  others,  some  much 
paler  than  others.  The  smaller  examples  generally 
possess  one  nucleus  occupying  the  greater  part  of  the 
corpuscle,  the  larger  ones  usually  include  two,  three, 
or  even  more  nuclei,  and  show  more  decided 
amoeboid   movement   than   the   others.     Division  by 


Chap,  ii.]  Blood.  15 

cleavage  of  the  white  corpuscles  of  the  blood  of  lower 
vertebrates  has  been  directly  observed  by  Klein  and 
Ranvier. 

15.  In  every  microscopic  specimen  of  the  blood 
of  man  and  mammals  are  found  a  variable  number 
of  large  granules,  more  or  less  angular,  singly  or  in 
groups,  which  have  been  specially  studied  by  Osier. 
According  to   Bizzozero  they  are,  when 

observed  in  the  living  and  fresh  blood,  \J      a 

pale,    circular,     or    slightly    oval    discs  -^  Q 

(Fig.  12,  b).      Their  size  is  only  \  to  \  VJ 
of    that    of    the    red    blood    corpuscles.  & 

They  are  called  by  him  blood  plates,  and  *    ° 

i  ,1  ,        -i  n  x-    i     ■  Fig.  12.— Human 

he  supposes  them  to  be  01   essential  1m-       e  siood. 
portance  in  the  coagulation  of  the  blood,     %^es^°&°uood 
in    fact,    the    fibrin    ferment.       Hay  em       ^es  of  Bizzo- 
described  them    previously   as  being  in- 
termediate  forms  in  the  development  of   red  blood 
corpuscles,  and  called  them  hsematoplasts. 

16.  Development  of  Blood  Corpuscles.— 
At  an  early  stage  of  embryonal  life,  when  blood 
makes  its  appearance  it  is  a  colourless  fluid,  contain- 
ing only  white  corpuscles  (each  with  a  nucleus),  which 
are  derived  from  certain  cells  of  the  mesoblast.  These 
white  corpuscles  change  into  red  ones,  which  become 
flattened,  and  their  protoplasm  gets  homogeneous  and 
of  a  yellowish  colour.  All  through  embryonal  life  new 
white  corpuscles  are  transformed  into  red  ones.  In 
the  embryo  of  man  and  mammals  these  red  corpuscles 
retain  their  nuclei  for  some  time,  but  ultimately  lose 
them.  New  nucleated  red  blood  corpuscles  are,  how- 
ever, formed  by  division  of  old  red  corpuscles.  Such 
division  has  been  observed  even  in  adult  blood  of 
lower  vertebrates  (Peremeschko)  as  well  as  in  mammals 
(marrow  of  bone  by  Bizzozero  and  Torre). 

An  important  source  for  the  new  formation  of  red 
corpuscles  in  the  embryo  and  adult  is  the  red  marrow 


1 6  Elements  of' Histology.        [Chap.  hi. 

of  bones  (Neumann,  Bizzozero,  Rindfleisch),  in  which 
numerous  nucleated  protoplasmic  cells  (marrow  cells) 
are  converted  into  nucleated  red  blood  corpuscles.  The 
protoplasm  of  the  corpuscle  becomes  homogeneous  and 
tinged  with  yellow,  the  nucleus  being  ultimately  lost. 
The  spleen  is  also  assumed  to  be  a  place  for  the  forma- 
tion of  red  blood  corpuscles.  Again,  it  is  assumed  that 
ordinary  white  blood  corpuscles  are  transformed  into 
red  ones,  but  of  this  there  is  no  conclusive  evidence. 
In  all  these  instances  the  protoplasm  becomes  homo- 
geneous and  filled  with  haemoglobin,  while  the  cell 
grows  flattened,  discoid,  and  the  nucleus  in  the  end 
disappears. 

Sch'afer  described  intracellular  (endogenous)  for- 
mation of  red  blood  corpuscles  at  first  as  small  haemo- 
globin particles,  but  soon  growing  into  red  blood  cor- 
puscles, in  certain  cells  of  the  subcutaneous  tissue  of 
young  animals.  Malassez  describes  the  red  blood  cor- 
puscles originating  by  a  process  of  continued  budding 
from  the  marrow  cells. 

The  white  corpuscles  appear  essentially  to  be 
derived  from  the  lymphatic  organs,  whence  they  are 
carried  by  the  lymph  into  the  circulating  blood. 


CHAPTER     III. 

EPITHELIUM. 

17.  Epithelial  cells  (Fig.  13a)  are  nucleated  proto- 
plasmic cells ■,  forming  continuous  masses  on  the  surface  of 
the  skin,  of  the  lining  membrane  of  the  alimentary  canal, 
the  respiratory  organs,  the  urinary  and  genital  organs, 
the  free  surface  of  the  conjunctiva,  and  the  anterior 
surface  of  the  cornea.     The  lining  of  the  tubes  and 


Chap.  III.] 


Epithelium. 


i7 


alveoli  of  secreting  and  excreting  glands,  such  as  the 
kidney,  liver,  mammary  gland,  testis  and  ovary,  the 
salivary  glands,  mucous,  peptic,  and  Lieberkiihn's 
glands,  the  sweat  and  sebaceous  glands,  the  hair 
follicles,  &c,  consists  of  epithelial  cells.  Such  is  the 
case  also  with  the  sensory  or  terminal  parts  of  the 
organs  of  the  special  senses.  And,  finally,  epithelial 
cells  occur  in  other 
organs,  such  as  the 
thyroid  gland,  the 
pituitary  body,  &c. 
The  hairs  and 
nails,  the  cuticle  of 
the  skin,  certain 
parts  of  the  rods 
and  cones  of  the 
retina,  and  the  rods 
of  corti  of  the  organ 


ft 


~M 


A,  Columnar  cells  of  intestine;  B,  polyhedral 
cells  of  the  conjunctiva ;  c,  ciliated  conical 
cells  of  the  trachea ;  d,  ciliated  cell  of  frog's 
mouth;  E,  inverted  conical  cell  of  trachea; 
F,  squamous  cell  of  the  cavity  of  mouth,  seen 
from  its  hroad  surface  ;  G,  squamous  cell,  seen 
from  its  narrow  side. 


of  hearing,  are  modi- 
fied epithelial  struc- 
tures. 

Epithelial     cells 

are  grouped  together     ¥ig,  i3A._Various  kinds  of  Epithelial  Cells 

by  exceedingly  thin 
layers  of  an  albu- 
minous interstitial 
cement  substance, 
which  during  life  is 

of  a  semi-fluid  nature,  and  belongs  to  the  group  of 
bodies  known  as  globulins. 

18.  As  regards  shape  we  distinguish  two  kinds 
of  epithelial  cells — columnar  and  squamous.  The 
columnar  cells  are  short  or  long,  cylindrical  or  pris- 
matic, pyramidal,  conical,  club-shaped,  pear-shaped, 
or  spindle-shaped ;  their  nucleus  is  always  more  or 
less  oval,  their  protoplasm  more  or  less  longitudinally 
striated.  On  the  free  surface  of  the  cells — i.e.,  the 
c 


i8 


Elements  of  Histology. 


[Chap.  III. 


part  facing  a  cavity,  canal,  or  general  surface — in  many- 
instances  a  bright  thinner  or  thicker  cuticular  struc- 
ture is  seen,  with  more  or  less  distinct  vertical  striation. 
The  conical  or  spindle-shaped,  club-shaped,  and  pear- 
shaped  cells  are  drawn  out  into  longer  or  shorter 
single  or  branched  extremities; 

The  squamous  or  pavement  cells  are  cubical, 
polyhedral  or  scaly.  The  nucleus  of  the  former  is 
almost  spherical  that  of  the  latter  flattened  in  propor- 
tion to  the  thinness  of  the  scales.  In  polyhedral 
cells  it  can  be  occasionally  perceived  that  the  granula- 
tion is  due  to  the  regular  honeycombed  nature  of  the 
cell  protoplasm. 

19.  As  regards  size,  the  epithelial  cells  differ 
considerably  from  one  another  in  different  parts,  and 


even  in  the  same  part. 


Thus,  the  columnar  cells, 
covering  the  surface  of 
the  villi  of  the  small  in- 
testine, are  considerably 
longer  than  those  lining 
the  mucous  membrane  of 
the  uterus ;  the  columnar 
cells  lining  the  larger 
ducts  of  the  kidney  are 
considerably  longer  than 
those  lining  the  small 
ducts ;  the  polyhedral 
cells  covering  the  anterior 
surface  of  the  cornea  are  considerably  smaller  than 
those  on  the  surface  of  the  lining  membrane  of  the 
urinary  bladder;  the  scales  lining  the  ultimate  recesses 
of  the  bronchial  tubes — the  air  cells — are  considerably 
smaller  than  those  on  the  surface  of  the  membrane 
lining  the  human  oral  cavity  and  oesophagus. 

20.  As  regards  arrangement,  the  epithelial  cells 
are  either  arranged  as  a  single  layer  or  are  stratified, 
forming  several  superimposed  layers;  in  the  former  case 


13b.— Three  Mucus-secreting 
Goblet  Cells. 

A,  From  the  stomach  of  newt ;  b,  from 
a  mucous  gland  ;  c,  from  the  surface 
of  the  mucous  membrane  of  the  in 
testine. 


chap,  in.]  Epithelium.  19 

we  have  a  simple  in  the  latter  a  stratified  epithelium. 
The  simple  epithelium  may  be  composed  of  squamous 
cells — simple  squamous  or  simple  pavement  epithe- 
lium— or  it  may  be  composed  of  columnar  cells — 
simple  columnar  epithelium.  The  stratified  epithelium 
may  be  stratified  pavement,  or  stratified  columnar ; 
in  the  former  case  all  or  the  majority  of  the  layers 
consist  of  squamous  or  polyhedral  cells,  in  the  latter 
all  cells  belong  to  the  columnar  kind.  Simple 
squamous  epithelium  is  that  which  lines  the  air 
cells,  certain  urinary  tubules  of  the  kidney  (the  looped 
tubes  of  Henle,  the  cortical  parts  of  the  collecting 
tubes),  the  acini  of  the  milk-gland,  the  inner  surface 
of  the  iris  and  choroid  membrane  of  the  eyeball. 
Simple  columnar  epithelium  is  that  on  the  inner 
surface  of  the  stomach,  small  and  large  intestine, 
uterus,  small  bronchi,  ducts  and  acini  of  mucous  and 
salivary  glands,  of  some  kidney  tubules,  &c.  Stratified 
pavement  epithelium  is  that  on  the  epidermis,  the 
epithelium  lining  the  cavity  of  the  mouth,  pharynx, 
and  oesophagus  in  man  and  mammals,  the  anterior 
surface  of  the  cornea,  &c. 

21.  The  epidermis  (Fig.  14)  consists  of  the  fol- 
lowing layers  : — (a)  Stratum  corneum :  this  is  the  super- 
ficial stratum,  and  it  consists  of  several  layers  of  horny 
scales,  without  any  nucleus.  The  layers,  which  are 
separated  from  one  another  by  narrow  clefts  contain- 
ing air,  are  then  in  process  of  desquamation.  This 
stratum  is  thickest  on  the  palm  of  the  hand  and 
fingers,  and  the  sole  of  the  foot,  (b)  The  stratum 
lucidum,  composed  of  several  dense  layers  of  horny 
scales,  in  which  traces  of  an  exceedingly  flattened 
nucleus  may  be  perceived,  (c)  Then  follow  many 
layers  of  nucleated  cells,  forming  the  stratum  or 
rete  Malpighii  or  rete  mucosum.  The  most  super- 
ficial layer  or  layers  of  it  are  flattened  scales,  which 
are  characterised  by  the  presence  around  the  nucleus 


20 


Elements  of  Histology. 


[Chap.  III. 


a,  The  stratum  Malpighii ;  6,  the  stratum  granulosum  ; 
c,  the  stratum  lucidum ;  d,  the  stratum  corneum. 
(Atlas.) 


of  globular  or  elliptical  granules  of  the  nature  inter- 
mediate between  protoplasm  and  keratin.  Their  sub- 
stance is  called 
eleidin  (Ran- 
vier)  ;  these 
cells  form  the 
granular  layer 
(stratum  gra- 
nulosum) of 
Langerhans. 
Deeper  down 
the  cells  be- 
come less  flat- 
tened and  more 

Fig.  14.-From  a  Verticaljection  through  the    polyhedral,  and 

the  deepest 
form  a  layer  of 
more  or  less 
columnar  cells,  placed  vertically  on  the  surface  of 
the  subjacent  corium. 
The  substance  of  the 
hairs,  nails,  claws,  hoofs, 
consists  of  h©rny  scales. 
(See  chapter  on  Skin.) 

22.  The  stratified 
pavement  epithe- 
lium (Fig.  15)  lining  the 
cavity  of  the  mouth,  the 
surface  of  the  tongue,  the 
pharynx  and  oesophagus 
of  man  and  mammals,  and 
the  anterior  surface  of  the 

cornea,  &c,  is  as  regards  Fig   15_From  a  ~ertieBjl  se^tien 
the    style    and    arrange- 
ment of  the  cells,  identi- 
cal   with     the     stratum 
Malpighii  of  the  epider- 


through  the  anterior  layers  of  the 
Cornea. 

a,  The  stratified  pavement  epithelium  ; 
b,  the  substantia  propria,  with  the 
corneal  corpuscles  between  itslamellie. 
(Handbook.) 


Chap.  1 1 i.i  Epithelium.  21 

mis.  The  cell  protoplasm  is  more  transparent  in  the 
former,  and  the  granular  cells  of  the  stratum  granu- 
losum  are  not  always  present,  but  they  generally  are 
in  the  epithelium  of  the  tongue  and  of  the  rest  of  the 
oral  cavity.  The  most  superficial  scales  show  more  or 
less  horny  transformation. 

23.  Stratified  columnar  epithelium  is  met 
with  on  the  lining  membrane  of  the  respiratory 
organs,  as  larynx,  trachea,  and  large  bronchi.  It 
consists  of  several  layers  of  columnar  cells :  a  super- 
ficial layer  of  conical  or  prismatic  cells,  with  a  more 
or  less  pointed  extremity  directed  towards  the  depth  , 
between  these  are  inserted  spindle-shaped  cells,  and 
finally  inverted  conical  cells. 

The  epithelium  of  the  ureter  and  bladder  is  called 
transitional  epithelium.  It  is  stratified,  and  the  most 
superficial  layer  consists  of  squamous  cells.  Under- 
neath this  is  a  layer  of  club-shaped  cells,  between 
which  extend  one  or  more  layers  of  small  spindle- 
shaped  cells. 

Amongst  the  columnar  epithelial  cells  occurring 
in  man  and  mammals  the  ciliated  cells  and  the  goblet 
cells,  and  amongst  the  squamous  cells  the  prickle  cells, 
deserve  special  attention. 

24.  Ciliated  cells  are  characterised  by  possess- 
ing a  bundle  of  very  fine  longer  or  shorter  hairs  or 
cilia  on  their  free  surface.  These  cilia  are  direct  pro- 
longations of  the  cell  protoplasm.  More  correctly 
speaking,  the  cilia  are  continuous  with  the  filaments 
or  striae  of  the  cell  protoplasm.  The  superficial  layer 
of  conical  cells  of  the  epithelium  in  the  respiratory 
organs,  the  columnar  cells  lining  the  uterus  and  ovi- 
duct, and  the  columnar  cells  lining  the  tubes  of  the 
epididymis  possess  such  cilia.  In  lower  vertebrates 
the  ciliated  cells  are  much  more  frequently  observed ; 
in  Batrachia  the  epithelial  cells  lining  the  mouth, 
pharynx,  and  oesophagus  are  ciliated. 


22  Elements  of  Histology.        [Chap.  hi. 

While  fresh  in  contact  with  the  membrane  which 
they  line,  or  even  after  removal  from  it,  provided 
the  cells  are  still  alive,  the  ciliated  cells  show  a  rapid 
synchronous  whip-like  movement  of  their  cilia,  the 
cilia  of  all  cells  moving  in  the  same  direction.  The 
movement  ceases  on  the  death  of  the  cell,  but  may 
become  slower  and  may  cease  owing  to  other  causes 
than  death,  such  as  coagulation  of  mucus  on  the 
surface,  want  of  sufficient  oxygen,  presence  of  car- 
bonic acid,  low  temperature,  &c.  Under  these  circum- 
stances, removal  of  the  impediment  will  generally 
restore  the  activity  of  the  cilia.  Moderate  electric 
currents  and  heat  stimulate  the  movement,  strong 
electric  currents  and  cold  retard  it.  Reagents  fatally 
affecting  cell  protoplasm  also  stop  permanently  the 
ciliary  action. 

25.  Goblet  or  chalice  cells  (Figs.  13b,  16)  are 
cells  of  the  shape  of  a  conical  chalice.  The  pointed  part 
is  directed  away  from  the  free  surface, 
and  contains  a  compressed  triangular 
nucleus,  surrounded  by  a  trace 
of  protoplasm.  The  body  of  the 
v!?m  16'  ,  „        goblet  contains  mucus.      This  latter 

From  a  Vertical  Sec-      ° 

tion   through   the     may   be   in  various  states    ot  iorma- 

Epitheliurn   on   the       .  •  n  ■  •  i  i 

surface  of  the  niu-    tion,  and  may  at  any  time  be  poured 

cous   membrane  of  7  ,         •>  *  f 

the  large  intestine.      out     01     the     Cell.         Goblet    Cells     are 

^een pouring outttfeir    most   commonly   met   with   amongst 

ord^ary  Thecofumnl?     the  epithelium  lining  the  respiratory 

organs,  the  surface  of  the  stomach  and 

intestines,  and  especially  in  mucous  glands,  in  whose 

secreting  portion  all  cells  are  goblet  cells. 

The  protoplasm  of  columnar  cells  facing  a  free 
surface,  no  matter  whether  in  simple  or  stratified 
epithelium,  ciliated  or  non-ciliated,  may  undergo 
such  alteration  as  will  lead  to  the  transforma- 
tion of  the  cell  into  a  goblet  cell.  This  takes 
place    during    life,    and,    in   fact,    represents  an  im- 


Chap,  in.]  Epithelium.  23 

portant  function  of  columnar  epithelial  cells — viz., 
the  formation  of  mucus.  In  mucus-secreting 
glands  all  the  epithelial  cells  have  this  function 
permanently,  but  in  ordinary  columnar  epithelium 
only  a  comparatively  small  number  of  the  cells, 
as  a  rule,  undergo  this  change,  and  then  only 
temporarily ;  for  a  cell  subject  to  it  at  one  time  may 
shortly  afterwards  resume  the  original  shape  and 
aspect  of  an  ordinary  protoplasmic,  cylindrical,  or 
conical  epithelial  cell,  and  vice  versa.  If  ciliated 
cells  undergo  this  change,  the  cilia  are  generally  first 
detached. 

It  can  be  shown  that  in  this  change  of  an  ordinary 
columnar  epithelial  cell  into  a  goblet  cell,  the  inter- 
stitial substance  of  the  cell  reticulum  increases  in 
amount,  the  meshes  enlarging  and  distending  the  body 
of  the  cell.  The  interstitial  substance  probably  under- 
goes the  change  into  mucin. 

26.  Prickle  Cells  (Fig.  14). — Amongst  the  middle 
and  deeper  layers  of  the  stratified  pavement  epithelium, 
such  as  is  present  in  the  epidermis  and  on  the  surface 
of  the  oral  cavity  and  pharynx,  we  meet  with  a  close, 
more  or  less  distinct  and  regular  striation,  extending 
from  the  margin  of  one  cell  to  that  of  each  of  its 
neighbours,  by  means  of  fine  transverse  short  fibrils 
which,  passing  from  protoplasm  to  protoplasm,  connect 
the  surfaces  of  the  cells, 

27.  Pigmented  epithelial  cells — i.e.,  epithelial  cells 
filled  with  black  pigment  particles  (crystals) — are  found 
on  the  internal  surface  of  the  choroid  and  iris  of 
the  eyeball. 

In  coloured  skins,  and  in  coloured  patches  of  skin 
and  mucous  membrane,  such  as  occur  in  man  and 
animals,  there  is  found  pigment  in  the  shape  of 
granules  lodged  in  the  protoplasm  of  the  deeper 
epithelial  cells,  as  well  as  in  branched  cells  situated 
between  the  epithelial  cells  of  the  deeper  layers.  Minute 


24  Elements  of  Histology.        rchap.  in. 

branched  non-pigmented  nucleated  cells  are  met  with 
in  the  interstitial  or  cement  substance  of  various  kinds 
of  epithelium,  simple  and  stratified,  e.g.,  epidermis, 
epithelium  of  oral  cavity,  cornea,  &c. 

28.  Epithelial  cells  undergo  division,  and  by  this 
means  a  constant  regeneration  takes  place.  In  those 
parts  where  the  loss  of  the  superficial  layers  of  cells  is 
conspicuous,  such  as  the  epidermis,  the  stratified  epi- 
thelium of  the  tongue  and  oral  cavity,  the  sebaceous 
follicles  of  hairs,  the  regeneration  goes  on  more 
copiously  than  at  places  where  no  such  conspicuous  loss 
occurs— as,  for  instance,  in  the  stomach  and  intestines, 
the  secreting  glands,  or  sense  organs. 

In  the  stratified  pavement  epithelium  it  is  the  cells 
of  the  deepest  layer  which  chiefly  divide ;  the  next 
layer  thereby  becomes  gradually  shifted  towards  the 
surface,  and  more  flattened,  and  on  reaching  the  surface 
dries  up  owing  to  rapid  loss  of  water. 

29.  The  interstitial  substance  between  the  epi- 
thelial cells  being  soft  and  semi-fluid,  and  the  proto- 
plasm of  the  epithelial  cells  themselves  being  a  soft 
flexible  material,  it  is  possible  for  the  cells  to  change 
their  shape  and  arrangement  after  pressure  and  tension, 
exerted  on  them  by  the  contraction  or  distension  of  the 
membrane  on  which  they  are  situated.  Thus,  for  in- 
stance, the  epithelium  lining  a  middle-sized  bronchus 
may  appear  at  one  time  as  composed  of  long,  thin, 
columnar  epithelial  cells  in  two  layers ;  at  another,  as 
a  single  layer  of  long  columnar  cells ;  or  again  as 
a  single  layer  of  polyhedral  or  short  columnar  cells  : 
the  first  is  the  case  when  the  bronchus  is  contracted, 
the  second  when  it  is  in  a  medium  state  of  distension, 
the  third  when  it  is  much  distended.  Similar  changes 
may  be  noticed  on  the  epithelium  lining  the  mucous 
membrane  of  the  bladder,  gland  tubes,  the  epidermis, 
and  various  other  epithelial  structures. 


Chap.  IV.]  25 


CHAPTER    IV. 

ENDOTHELIUM. 

30.  The  free  surfaces  of  the  serous  and  synovial 
membranes,  and  of  those  of  the  brain  and  spinal 
cord,  the  posterior  surface  of  the  cornea  and  anterior 
surface  of  the  iris,  the  surfaces  of  tendon  and  tendon- 
sheaths,  the  lymph  sinuses  or  lymph  sacs  of  amphibian 
animals,  the  cavity  of  the  heart,  of  blood-vessels 
and  of  lymphatic-vessels  are  lined  with  a  continuous 
endothelial  membrane,  composed  of 
d  single  layer  of  flattened  trans- 
parent squamous  cells,  called  endo- 
thelial cells  (Fig.  17).  Each  contains 
an  oval  nucleus,  situated  generally 
excentrically.  Just  as  in  the  case 
of  epithelium,  the  endothelial  cell  Kg.  llTm^Set}Tt 
plates  are  joined  by  a  fluid  or  semi-  Cat- 
fluid     homogeneous    interstitial    or    ^henai^ens!  tanVathe 

,  7     ,  n      ,i  .  r»  nucleus   of    the   latter 

cement  substance  01  the  nature  or  are  weu  shown. 
globulin.  When  examining  any  of 
the  above  structures  fresh  the  endothelial  cells  are 
not,  as  a  rule,  visible,  owing  to  their  great  trans- 
parency; but  by  staining  the  structures  with  a 
dilute  solution  of  nitrate  of  silver,  and  then  ex- 
posing them  to  the  influence  of  the  light,  the  cement 
substance  appears  stained  black,  whereby  the  shape 
and  size  of  the  cell  plates  become  evident.  By  various 
dyes  also  the  nucleus  of  each  cell  plate  may  be  brought 
into  view. 

On  careful  examination,  and  with  suitable  re- 
agents, it  can  be  shown  that  each  endothelial  cell 
consists    of    a    homogeneous    ground-plate.      In    it 


26  Elements  of  Histology.         [Chap.  iv. 

lies  the  nucleus,  and  around  it  is  a  substance  which 
appears  granular,  but  which  is  of  a  fibrillar  nature, 
the  fibrillse  being  arranged  in  a  network,  and  extend- 


Fig.  18. — Network  of  Lymphatics  in  the  Central  'Tendon  of  the 
Diaphragm  of  Rabbit,  prepared  with  nitrate  of  silver,  so  as  to  show 
the  outlines  of  the  Endothelial  Cells  forming  the  wall  of  the 
Lymphatics. 

a,  Big  lymphatic  vessels;  b,  lymphatic  capillaries;  c,  apparent  ends  of  the 
capillaries.    (Handbook.) 

ing  in  many  places  up  to  the  margin  of  the  ground- 
plate.  The  nucleus  is  limited  by  a  membrane,  and 
contains  a  well-developed  reticulum.  The  fibrillse 
of  the  cell  substance  appear  in  connection  with  the 
nuclear  reticulum. 

31.  As  regards  shape,  endothelial  cells  differ 
considerably.  Those  of  the  pleura,  pericardium, 
peritoneum,  and  endocardium  of  man  and  mammals 


Chap.  IV.] 


EN  DO  THELIUM. 


27 


are  more  or  less  polygonal,  or  slightly  elongated.  Their 
outlines  Vary ;  in  the  lining  of  the  lymph  sacs  of  the 
frog  they  are  much  larger,  and  of  very  sinuous  out- 
line j  while  those  of  the  posterior  surface  of  the  cornea 


Fig.  19. — Omentiiin  of  Rabbit,  stained  with  Mtrate  of  Silver. 
a,  Ordinary  flat  endothelial  cells ;  b,  germinating  cells.    (Atlas.) 

are  very  regular,  pentagonal,  or  hexagonal,  having 
straight  outlines  in  the  perfectly  normal  and  well-pre- 
served condition,  but  serrated  and  sinuous  after  they 
have  been  prepared  with  various  reagents  and  in  the 
abnormal  state ;  the  endothelial  plates  lining  the  blood- 
vessels and  lymphatic  vessels  (Fig.  18)  are  narrow  and 
elongated,  with  more  or  less  sinuous  outlines.  In  the 
lymphatic  capillaries  the  endothelial  plates  are  poly- 
gonal, but  their  outline  serrated. 

32.  As  a  rule  the  endothelial  cells  are  flattened, 


28 


Elements  of  Histology. 


[Chap.  IV. 


i.e.,  scaly — but  in  some  places  they  are  polyhedral, 
or  even  short  columnar.  Such  cells  occur  isolated  or 
in  small  groups,  or  covering  large  and  small  patches, 
nodular,  villous,  or  cord-like  structures  of  the  pleura 


Fig.  20.— Part  of  Peritoneal  Surface  of  the  Central  Tendon  of  Diaphragm 
of  Babbit,  prepared  with.  Nitrate  of  Silver. 

8,  Stomata;  I,  lymph-channels ;  t,  tendon  bundles.  The  surface  is  covered  with 
endothelium.  The  stomata  are  surrounded  by  germinating  endothelial  cells. 
(Handbook.) 

and  omentum,  on  the  synovial  membranes,  tunica 
vaginalis  testis,  &c.  They  are  especially  observable 
in  considerable  numbers  in  the  pleura  and  omentum 
(Fig.  19)  of  all  normal  subjects  (human,  ape,  dog,  cat, 
and  rodent  animals);  their  number  and  frequency  of 
occurrence  are  increased  in  pathological  conditions 
(chronic  inflammations,  tuberculosis,  cancer,  &c). 

These  endothelial  cells  are  the  germinating  endo- 
thelial cells,  and   they   can  be   shown  to  be   in   an 


Chap.  IV.] 


EN  DO  T HELIUM. 


20 


active  state  of  division.  They  thus  produce  small 
spherical  lymphoid  (amoeboid)  cells,  which  ultimately 
are  absorbed  by  the  lymphatics,  and  carried  into  the 
blood  system  as  white  blood  corpuscles.     On  the  sur- 


Fig.  21.— Part  of  Omentum  of  Cat,  stained  with  Nitrate  of  Silver. 

o,  Fenestras  or  holes ;  b,  trabeculae  covered  with  endothelium.    Only  the  outlines 
(.silver-lines)  of  the  endothelial  cells  are  shown. 


face  of  the  serous  membranes,  especially  the  diaphragm 
(Fig.  20)  and  pleura,  there  exist  minute  openings, 
stomata,  leading  from  the  serous  cavity  into  a  lym- 
phatic vessel  of  the  serous  membrane.  These  stomata 
are  often  lined  by  germinating  cells. 

33.  In  the  frog,  germinating  cells  occur  in  great 
abundance  on  the  mesogastrium  and  the  part  of  the 
peritoneum  which  separates  the  peritoneal  cavity 
from  the  cisterna   lymphatica  magna.     This  part  of 


30  Elements  of  Histology.         [Chap.  iv. 

the  peritoneum  is  called  the  septum  cisternae  lym- 
phaticse  magnae,  and  on  it  occur  numerous  holes  or 
stomata,  by  which  a  free  communication  is  established 
between  the  two  cavities.  On  the  peritoneal  surface 
of  this  septum  the  stomata  are  often  bordered  by 
germinating  cells.  In  the  female  frog,  these  and 
other  germinating  endothelial  cells  of  the  peritoneum 
(mesogastrium,  mesenterium,  septum  cisternae)  are 
ciliated. 

34.  The  omentum  and  parts  of  the  pleura  are,  in 
the  adult  human  subject,  ape,  dog,  cat,  guinea-pig,  rat, 
&c,  of  the  nature  of  a  fenestrated  membrane  (Fig  21), 
bands  of  fibrous  tissue  of  various  sizes  dividing  and 
reuniting,  and  leaving  between  them  larger  or  smaller 
holes,  in  shape  oblong  or  circular.  These  holes 
or  fenestras  are  not  covered  with  anything,  the  endo- 
thelial cells  adhering  only  to  the  surfaces  of  the 
bands  without  bridging  over  the  fenestras  On  the 
peritoneal  surface  of  the  diaphragm  the  endothelial 
cells  possess  a  different  arrangement  from  that  on 
the  pleural  side ;  on  the  former  surface  a  number  of 
lymph  channels  (that  is,  clefts  between  the  bundles 
of  tendon  and  muscle)  radiate  towards  the  middle 
of  the  central  tendon.  The  endothelium  of  the  free 
surface  over  these  lymph  channels  is  composed  of 
much  smaller  cells  than  at  the  places  between, 
so  that  the  endothelium  of  the  peritoneal  surface  of 
the  diaphragm  shows  numbers  of  radiating  streaks 
of  small  endothelial  cells.  Many  of  these  small  cells 
are  not  flattened,  but  polyhedral,  and  of  the  nature 
of  germinating  cells  (Fig.  20.)  The  above-mentioned 
stomata  occur  amongst  these  small  endothelial  cells. 


Chap.  V.]  71 


CHAPTER   V. 

FIBROUS    CONNECTIVE    TISSUES. 

35.  By  the  name  of  "  connective  tissues "  we 
designate  a  variety  of  tissues  which  have  these  things 
in  common — that  they  are  developed  from  the  same 
embryonal  elements ;  that  they  all  more  or  less  serve 
as  supporting  tissue  or  framework,  or  connecting  sub- 
stance, for  nervous,  muscular,  glandular,  and  vascular 
tissues ;  that  they  are  capable  of  taking  one  another's 
place  in  the  different  classes  of  animals;  that  in  the 
embryo  and  in  the  growing  condition  one  may  be 
changed  into  the  other ;  and  that  in  the  adult  they 
gradually  shade  off  one  into  the  other. 

Connective  tissues  are  divided  into  the  three  great 
groups  of  (1)  fibrous  connective  tissue;  (2)  cartilage; 
(3)  bone,  to  which  may  be  added  dentine.  Each  of 
these  is  subdivided  into  several  varieties,  as  will 
appear  farther  on,  but  in  all  instances  the  ground 
substance,  or  matrix,  or  intercellular  substance,  is 
to  be  distinguished  from  the  cells.  In  the  fibrous  con- 
nective tissue  the  matrix  yields  glutin  or  gelatin,  and 
the  cells  are  called  connective  tissue  cells,  or  connective 
tissue  corpuscles.  In  the  cartilage  the  ground  sub- 
stance yields  chondrin,  and  the  cells  are  called  carti- 
lage cells.  In  the  third  group  the  ground  substance 
contains  inorganic  lime  salts,  intimately  connected 
with  a  fibrous  matrix,  and  the  cells  are  called  bone 
cells. 

36.  The  fibrous  connective  tissue,  or  white 
fibrous  tissue,  occurs  in  the  skin  and  mucous 
membranes,  in  the  serous  and  synovial  membranes, 
in  the  membranes  of  the  brain  and  spinal  cord,   in 


32 


Elements  of  Histology. 


[Chap.  v. 


tenaons  and  tendon  sheaths,  in  fasciae  and  aponeuroses, 
in  the  intermuscular  tissue,  and  in  the  tissue  con- 
necting neighbouring  organs,  &c.  It  consists  of 
microscopic  band-like  or  cylindrical  bundles  or  fasciculi 
of  exceedingly  fine  homogeneous  fibrils  (Fig.  22),  which 
are  known  as  the  elementary  connective  tissue  fibrils. 


Fig.  22.- 


-Plexus  of  Bundles  of  Fibrous  Tissue  from  the  Omentum 
of  Eat. 


a,  A  capillary  blood  vessel ;  6,  bundles  of  fibrous  tissue ;  c,  the  connective-tissue 
corpuscles;  d, plasma  cells.    (Atlas.) 


According  to  the  number  of  these  the  bundles  differ 
in  size.  The  bundles,  and  also  their  constituent 
fibrils,  may  be  of  very  great  length — several  inches. 
Where  the  fibrous  tissue  forms  continuous  masses — 
as  in  tendon,  fascia,  aponeurosis,  skin,  and  mucous 
membrane — the  microscopic  bundles  are  aggregated 
into  smaller  or  larger  groups,  the  trabeculce,  and  these 
are  again  associated  into  groups.  The  fibrils  are  held 
together  by  an  albuminous  (globulin),  semi-fluid,  homo- 
geneous cement  substance,  which  is  also  present  between 
the  bundles  forming  a  trabecula. 

On  adding  an  acid  or  an  alkali  to  a  bundle  of 


chap,  v.]      Fibrous  Connective  Tissues.  33 

fibrous  tissue,  it  is  seen  to  swell  up  and  to  become 
glassy-looking,  homogeneous,  and  gelatinous.  Sub- 
jected to  boiling  in  water,  or  to  digestion  by  dilute 
acids,  the  bundles  of  fibrous  tissue  yield  glutin  or 
gelatin. 

37.  According  to  the  arrangement  of  the  bundles, 
the  fibrous  connective  tissue  varies  in  different  locali- 
ties. (1)  In  tendons  and  fasciae  the  bundles  are 
arranged  parallel  to  one  another.  (2)  In  the  true 
skin  and  mucous,  serous,  and  synovial  membranes,  in 
the  dura  mater  and  tendon  sheaths,  the  trabecule  of 
bundles  divide  repeatedly,  cross  and  interlace  very 
intimately  with  one  another,  so  that  thereby  a  dense 
felt-work  is  produced.  (3)  In  the  subcutaneous,  sub- 
mucous, or  subserous  tissue,  in  the  intermuscular  tissue, 
in  the  tissue  connecting  with  one  another  different 
organs  or  the  parts  of  the  same  organ — i.e.,  interstitial 
connective  tissue — the  texture  of  the  fibrous  tissue  is 
more  or  less  loose,  the  trabecular  dividing  and  re- 
uniting and  crossing  one  another,  but  leaving  between 
them  larger  or  smaller  spaces,  cellulse  or  areolae,  so 
that  the  tissue  assumes  the  character  of  a  loose 
plexus,  which  is  sometimes  called  "  areolar  "  or  "  cel- 
lular tissue."  Such  tissue  can  be  more  or  less  easily 
separated  into  larger  or  smaller  lamellae,  or  plates  of 
trabecular  (4)  In  the  omentum  and  parts  of  the 
pleura  of  man,  ape,  dog,  cat,  and  some  rodents,  and 
in  the  subarachnoidal  tissue  of  the  spinal  cord  and 
brain,  the  trabeculae  form  &  fenestrated  membrane,  with 
larger  or  smaller  oval  or  circular  holes  or  fenestrae. 

38.  The  connective  tissue  cells  or  corpuscles 
occurring  in  white  fibrous  tissue  are  of  several  varie- 
ties, (a)  In  tendon  and  fasciae  the  cells  are  ealled 
tendon  cells  or  tendon  corpuscles;  they  are  flattened 
nucleated  protoplasmic  cells  of  a  square  or  oblong 
shape  (Fig.  23a),  forming  continuous  rows  (single  files), 
situated  on  the  surface  of  groups  of  bundles  of  fibrous 


34 


Elements  of  Histology. 


[Chap.  v. 


tissue.  Between  these  groups  are  wider  or  narrower 
channels — the  interfascicular  spaces — running  parallel 
with  the  long  axis  of  the  tendon  (Fig.  23b).  The  cells 
in  each  row  are  separated  from  one  another  by  a  narrow 
line  of  albuminous  cement  substance,  and  the  round 
nucleus  of  the  cell  is  generally  situated  at  one  end,  in 

such  a  way  that  in  two 
adjacent  cells  of  the  grow- 
ing tendon  the  nuclei 
face  each  other.  This 
indicates  that  the  indi- 
vidual cells  undergo  divi- 
sion. Corresponding  to 
the  margin  of  each  row, 
the  cells  possess  minute 
processes.  The  cell  plate 
is  not  quite  flat,  but  pos- 
sessed of  one,  two,  or  even 
three  membranous  projec- 
tions, by  winch  it  is 
wedged  in  between  the 
individual  bundles  of  the 
group  to  which  the  row 
of  cells  belongs. 

39.  (h)  In  the  serous 
membranes,  cornea,  subcu- 
taneous tissue,  and  loose 
connective  tissues,  tne  cells  are  flattened  transparent 
corpuscles,  each  with  an  oblong  flattened  nucleus,  and 
more  or  less  branched  and  connected  by  their  processes. 
In  the  cornea  they  are  spoken  of  as  the  corneal  cor- 
puscles, and  are  very  richly  branched  (Fig.  25).  They 
are  situated  between  the  lamella?  of  fibrous  bundles  of 
which  the  ground  substance  of  the  cornea  consists. 

These  corpuscles  are  also  situated  in  the  interfasci- 
cular spaces,  or  spaces  left  between  the  bundles  of  the 
ground  substance,  which  are  cavities  in  the  interstitial 


Fig.  23a.— From  a  Tendon  of  Tail 
of  Monse,  showing  the  Tendon 
cells.  (The  tendon  is  viewed  in 
the  long  axis). 

a,  The  tendon  cells  seen  from  their 
broad  surface ;  6,  the  same  seen  side- 
ways.   (Handbooks 


chap,  v.]      Fibrous  Connective  Tissues. 


35 


substance  cementing  the  bundles  and  trabecule  together 
(von  Eecklinghausen).  In  the  cornea  and  serous  mem- 
branes these  spaces 
possess  the  shape 
of  branched  lacu- 
nas, each  lacuna 
being  the  home 
of  the  body  of 
the  cell,  "while  the 
branches  or  cana- 
liculi  contain  its 
processes.  These 
canaliculi  form  the 
channels  by  which 
neighbouring  lacu- 
nas anastomose 
with  one  another 
(Fig.  26).  The  ceU 
and  its  processes  do 
not  fill  up  the  la- 
cuna and  its  canali- 
culi. In  loose  connective  tissue  the  lacuna  may  be  of 
considerable  size,  and  may  contain  several  connective 

cells,  which  make  as  it 
were  a  lining  for  it. 
These  in  some  places  are 
very  little  branched,  and 
almost  form  a  continuous 
endotheloid  membrane  of 
flattened  cells.  Such  is 
the  subepithelial  endothe- 
lium of  Debove,  occur- 
ring underneath  the  epi- 
thelium on  the  surface 
of    the  bronchi,  bladder. 


Fig.  23b. — From  a  Transverse  Section  throna-h 
the  Tendons  of  the  Tail  of  a  Mouse,  stained 
with  gold  chloride. 

Several  fine  tendons  are  shown  here.  The  dark 
branched  corpuscles  correspond  to  albuminous 
cement  substance  stained  with  gold  chloride : 
thev  are  the  channels  between  the  bundles  of 
fibrous  tissue,  constituting  the  tendon,  and  seen 
here  as  the  clear  spaces  in  cross  section.  In  each 
of  these  channels  is  a  row  of  tendon  cells — not 
discernible  here,  the  long  axis  of  these  rows 
being  parallel  with  the  long  axis  of  the  tendon. 
(.Handbook.) 


Fig.  24.— From  the  Tail  of  a 
Tadpole. 

c,  Branched  connective  tissue  cells ; 
a  migratory  cell.    (Atlas.) 


membrane 


of   the  mucous 
and  intestines. 

40.  (c)  In  the  true 


skin  and  mucous  membranes 


36 


Elements  of  Histology. 


[Chap.  v. 


the  connective  tissue  cells  are  also  branched  flattened 

corpuscles,  and  by  their  longer 
£— ^Ita  e$m*>     or   shorter    processes    are   con- 

nected into  a  network  (Fig.  24). 
4'  Each  cell  has  a  flattened  oblong 

nucleus.  As  a  rule,  some  of 
the  processes  are  membranous 
prolongations  coming  off  under 
an  angle  from  the  body  of  the 
cell,  which  is  then  called  the 
chief  plate,  the  processes  being 
the  secondary  plates.  By  the 
latter    the    cell   is   wedged    in 

Fiff 'l^^owi^S  between  the  bundles  of  tiie  tra- 

Networks  of  theBranched    becula  to  which  it  belongs. 

This  character  of  the  cells 
(i.e.,  of  possessing  secondary 
plates)   is    well    shown    by  the 


Corneal  Corpuscles. 

The  network  of  their  pro- 
cesses ;  b,  nucleus  of  the 
corpuscle.    (Atlas.) 


cells  of  the  skin  and 
mucous  membranes, 
but  only  in  a  very 
limited  degree  by 
those  of  the  cornea 
and  serous  mem- 
branes, and  somewhat 
better  by  some  of 
those  of  the  subcuta- 
neous and  other  loose 
connective  tissues. 

In  the  skin  and 
mucous  membranes 
also  the  cells  and 
their  processes  are 
situated  in  the  in- 
terfascicular spaces. 

41.  The  connec- 
tive tissue  corpuscles 


Fig.  26.— From  the  Cornea  of  Kitten, 
stained  with  Nitrate  of  Silver,  show- 
ing the  Lymph-canal  System. 

a,  The  lacunae,  each  containing  the  nucleated 
cell-body,  just  indicated  here ;  6,  the 
canaliculi  for  the  cell  processes.    (Atlas.) 


Chap,  v.]      Fibrous  Connective  Tissues.  37 

hitherto  mentioned  are  fixed  corpuscles  ;  they  do  not 
show  movement.  Kiihne  and  Rollett  ascribe  to  the 
corneal  corpuscles  a  certain  amount  of  contractility,  in- 
asmuch as  they  are  said  to  be  capable  of  withdrawing 
their  processes  on  stimulation.  When  this  ceases  they 
are  said  again  to  protrude  them.  According  to  Strieker 
and  Norris,  they  acquire  contractility  when  the  corneal 
tissue  is  the  seat  of  inflammatory  irritation.  It  can 
be  shown  that  the  connective  tissue  cells  consist,  like 
the  endothelial  plates,  of  a  ground  plate  and  a  fibrillar 
reticulated  (granular-looking)  •  substance  around  the 
nucleus,  and  extending  beyond  the  ground  plate  into 
the  processes  of  the  cell. 

42.  Pigment  Cells. — In  the  lower  vertebrates, 
especially  fishes,  reptiles,  and  amphibian  animals,  we 
find  certain  branched  nucleated  connective  tissue  cor- 
puscles, distinguished  by  their  size  and  by  the  proto- 
plasm both  of  the  cell-body  and  processes — but  not  of 
the  nucleus — being  filled  with  pigment  granules.  The 
pigment  is  either  white  or  yellow,  or  more  commonly 
dark  brown  to  black.  These  cells  are  called  pigmented 
connective  tissue  cells,  or  simply  pigment  cells.  They 
are  very  numerous  in  the  skin  of  fishes,  reptiles,  and 
amphibian  animals,  and  also  around  and  between  the 
blood-vessels  of  the  serous  membranes.  They  are  also 
present  in  man  and  mammals,  but  then  they  are 
chiefly  limited  to  the  eye-ball,  where  they  occur  in  the 
proper  tissue  of  the  iris  of  all  but  albino  and  bright 
blue  eyes,  and  in  the  tissue  of  the  choroid  membrane. 
In  dark  eyes  of  mammals  a  large  number  of  these  cells 
are  found  in  the  tissue  between  the  sclerotic  and 
choroid,  as  the  lamina  fusca,  and  also,  but  to  a  more 
limited  degree,  in  the  sclerotic.  As  a  rule  they  appear 
to  be  of  various  kinds:  such  as  are  flattened,  large 
plates  perforated  by  a  number  of  small  and  large  holes 
and  minute  clefts ;  such  as  possess  a  more  spindle- 
shaped  body,  and  long,  thin,  not  very  richlv  branched 


38 


Elements  of  Histology. 


[Chap.  V. 


processes ;  and  intermediate  forms  between  the  two. 
But  on  careful  examination  it  will  be  seen  that  these 


CIlM! 


Fig<  27.— Pigment  Cells  of  the  Tail  of  Tadpole. 

A,  B,  c,  D  represent  various  states  ;  a  being  a  cell  in  an  uncontracted  or  passive 
state,  D  in  a  contracted  or  active  state. 


appearances  are  due  to  different  states  of  contraction 
of  the  same  kind  of  cells  (Fig.  27). 

43.  In  lower  vertebrates  the  dark  pigment  cells 
show  marked  contractility,  inasmuch  as  they  are 
capable  of  altogether  withdrawing  into  their  body  the 
pigmented  processes.      In  the  passive  state  these  are 


Chap,  v.]      Fibrous  Connective  Tissues.  39 

exceedingly  numerous,  and  form  a  network  so  dense 
that  the  whole  mass  of  cells  resembles  an  extremely 
close  network  of  pigment.  In  the  maximum  of 
activity  the  processes  disappear,  being  withdrawn  into 
the  cell-body,  which  now  looks  like  a  spherical  or 
oblong  mass  of  black  pigment.  Between  the  states 
of  passiveness  and  maximum  activity  there  are  various 
intermediate  grades,  in  which  the  pigmented  processes 
are  of  various  numbers  and  lengths. 

44.  Owing  to  the  great  number  of  the  pigment 
cells  in  the  skin  of  fishes  and  amphibian  animals,  the 
state  of  contraction  of  these  cells  materially  affects 
the  colour  of  the  skin.  If  the  dark  pigment  cells 
of  a  particular  part  contract,  the  skin  of  this  parti- 
cular part  will  become  lighter  and  brighter,  the  degree 
of  lightness  and  brightness  depending  on  the  degree 
of  contraction  of  the  pigmented  processes  by  the  cells. 
Briicke  has  shown  that  darkness  is  a  stimulus  to  the 
pigmented  cells  ;  they  contract,  and  the  skin  becomes 
light.  Sunlight  leaves  the  pigmented  cells  in  the 
passive  state,  i.e.,  the  skin  becomes  dark.  If  pre- 
viously they  have  been  contracted  by  darkness,  on 
being  exposed  to  sunlight  they  again  return  to  the 
passive  state.  The  contraction  of  the  pigment  cells 
is  under  the  direct  influence  of  the  nervous  system 
(Lister).  Pouchet  proved  that  the  contractility  of  the 
pigment  cells  of  the  skin  of  certain  fishes  is  influenced 
as  a  reflex  action  by  the  stimulation  of  the  retina  by 
light. 

45.  Fat  Cells. — Fat  cells  in  the  ripe  and  fully- 
formed  state  are  spherical,  relatively  large  vesicles, 
each  consisting  (a)  of  a  thin  protoplasmic  membrane, 
which  at  one  point  includes  an  oval  nucleus  flattened 
from  side  to  side,  and  (b)  of  a  substance,  which  is  an 
oil  globule  filling  the  cavity  of  the  vesicle  (Fig.  28). 
These  fat  cells  are  massed  together  by  fibrous  connective 
tissue  into  smaller  or  larger  groups,  which  in  their 


4° 


Elements  of  Histology 


[Chap.  v. 


turn  form  lobules;  these  again  become  lobes,  and 
these  make  continuous  masses.  Each  group  and 
lobule  has  its  afferent  arteriole,  one  or  two  efferent 
veins,  and  a  dense  network  of  capillaries  between ; 
each  mesh  of  the  capillary  network  holding  one, 
two   or   three   fat    cells.     (Fig.   49.)     Such   are   the 


Fig.  28. — From  a  Preparation  of  the  Omentum  of  Guinea-pig. 
a,  An  artery  ;  v,  vein ;  c,  young  capillary  blood-vessel ;  d,  fat  cells.    (Atlas.) 


nature  and  arrangement  of  the  fat  tissue  in  the 
subcutaneous  and  submucous  tissue,  in  the  serous  and 
synovial  membranes,  in  the  intermuscular  tissue,  in 
the  loose  tissue  connecting  organs  or  parts  of  organs. 
It  can  be  shown  that  fat  cells  are  derived  from 
ordinary  connective  tissue  cells.  In  some  places — 
both  in  the  embryo  and  adult — the  protoplasm  of  the 
connective  tissue  corpuscles  growing  in  size  becomes 
filled  with  small  oil  globules,  which,  increasing  in 
numbers,  become  fused  with  one  another  to  larger 
globules  ;  as  their  size  thus  increases  the  cell  nucleus 
becomes   shifted   to   the   periphery;    ultimately   one 


Chap,  v.]      Fibrous  Connective  Tissues.  41 

large  oil  globule  fills  the  cell,  and  what  is  left  of  the 
cell  protoplasm  surrounds  this  oil  globule  like  a 
membrane.  The  cell  as  a  whole  has  become  in  this 
process  many  times  its  original  size. 

46.  It  can  also  be  shown  that  where  at  one  time 
only  few  isolated  connective  tissue  corpuscles  are 
present,  at  another  time,  in  the  natural  state  of 
growth,  and  especially  under  very  favourable  condi- 
tions of  nutrition,  the  connective  tissue  cells  become 
increased  by  cell-multiplication  so  as  to  form  groups ; 
these  continue  to  increase  in  size  and  to  be  gra- 
dually furnished  with  their  own  system  of  blood- 
vessels; the  individual  cells  constituting  the  group 
become  then  converted  into  fat  cells,  and  their  pro- 
cesses are  thereby  lost. 

Individual  connective  tissue  cells  situated  in  the 
neighbourhood  of  small  blood-vessels  are  converted 
into  fat  cells  under  favourable  conditions  of  nutrition. 

In  starvation  the  fat  cells  lose  their  oil  globule, 
they  become  smaller  and  contain  a  serous  fluid,  which 
may  ultimately  also  disappear.  Finally,  the  fat  cell 
may  be  reduced  to  a  small,  solid,  protoplasmic,  slightly 
branched  celL 

47.  In  many  places  the  fibrous  connective  tissue 
includes,  besides  the  fixed  cells,  others  which  show 
amoeboid  movement.  These  are  of  two  kinds :  (1) 
migratory  or  wandering  cells.  These  are  identical 
with  colourless  blood  corpuscles  as  regards  size,  shape, 
aspect,  and  general  nature  (Fig.  24,  m).  They  wander 
about  through  the  spaces  of  the  fibrous  tissue.  Some 
of  them  are  slightly  larger,  and  possess  one  spherical 
relatively  large  nucleus.  The  amoeboid  movement 
of  these  cells  is  not  so  distinct  as  in  the  smaller 
variety.  (2)  Plasma  cells  of  Waldeyer.  They  are 
larger  than  the  former,  less  prone  to  migrating,  being 
possessed  of  only  slight  amoeboid  movement,  which 
is,  however,  sufficiently  pronounced  to  be  detected. 


42  Elements  of  Histology.  [Chap.  v. 

They  contain  always  coarse  granules,  which  are  com- 
posed of  a  substance  which  is  not  fat,  but  something 
between  protoplasm  and  fat.  They  stain  deeply  in 
dyes,  and  the  corpuscles  correspond  to  similar  "gra- 
nular "  corpuscles  of  the  blood.  These  ' '  granules  " 
may  change  into  fat  globules,  and  thus  the  plasma 
cell  becomes  transformed  into  a  fat  cell. 

48.  The  wandering  cells  occur  almost  in  all  loose 
fibrous  tissues,  chiefly  around  or  near  blood-vessels ; 
they  are  not  numerously  met  with  in  the  healthy 
state,  but  increase  greatly  in  the  state  of  inflamma- 
tion of  the  part.  The  larger  kinds  are  met  with 
in  certain  localities  only ;  in  the  sub-lingual  gland 
of  the  dog  and  guinea-pig  they  occur  in  numbers 
between  the  gland  tubes  or  acini.  They  are  also 
found  in  the  mucous  membrane  of  the  intestine. 
The  plasma  cells  are  met  with  chiefly  in  the  inter- 
muscular tissue,  in  the  mucous  and  sub-mucous  tissue 
of  the  intestine,  in  the  trabecule  of  the  lymphatic 
glands,  and  in  the  omentum. 

49.  Development  of  fibrous  tissue.— Fibrous 
connective  tissue  is  developed  from  embryonal  connec- 
tive tissue  cells,  i.e.,  from  spindle-shaped  or  branched 
nucleated  protoplasmic  cells  of  the  mesoblast.  The 
former  are  met  with  isolated  or  in  bundles,  as  in  the 
umbilical  cord  or  embryonal  tendon.  The  latter 
form  a  network,  as  in  the  fcetal  skin  and  mucous 
membrane.  In  both  instances  the  protoplasm  of  the 
embryonal  connective  tissue  cells  becomes  gradually 
transformed  into  a  bundle  of  elementary  fibrils, 
with  a  granular-looking  interstitial  substance.  The 
nucleus  of  the  original  cell  finally  disappears.  A 
second  mode  of  the  formation  of  fibrous  connective 
tissue  is  this  :  the  embryonal  connective  tissue  cell, 
while  growing  in  substance,  produces  the  fibrous  tissue 
at  the  expense  of  its  peripheral  part.  A  remnant  of 
the  protoplasm  persists  around  the  nucleus. 


Chap,  v.]      Fibrous  Connective  Tissues. 


43 


The  same  modes  of  formation  of  connective  tissue 
may  be  also  observed  in  the  adult  under  normal  and 
pathological  conditions. 

50.  Fibrous  connective  tissue  is  in  most  places 
associated  with  elastic  fibres  or  yellow  elastic  tissue. 
These  are  of  bright  aspect,  of  variable  thickness  and 
length,  branching 
and  anastomos- 
ing so  as  to  form 
networks  (Fig. 
29).  They  are 
straight  or  more 
or  less  twisted  ^ 
and  coiled.  The 
latter  condition 
may  be  observed 
when  the  tissue 
is  shrunk,  the 
former  when  it 
is  stretched. 
They  do  not 
swell  up  in  acids 
or  alkalies,  nor  Fi  29 
yield  glutin  or 
gelatin  on  boil- 
ing, but  contain 

a  chemically  different  substance,  viz.,  elastin. 
broken  their  ends  generally  curl  up. 

51,  Elastic  fibres  occur  in  great  numbers  as  net- 
works extending  between  the  bundles  of  fibrous  tissue, 
in  the  skin  and  mucous  membranes,  in  the  serous  and 
synovial  membranes,  and  in  the  loose  interstitial  con- 
nective tissues.  They  are  not  very  commonly  met 
with  in  tendons  and  fasciae ;  in  the  former  they  are 
seen  as  single  fibres  often  twisting  round  the  tendon 
bundles. 

Elastic  fibres  forming  bundles,  but  branched  and 


-From  a  Preparation  of  the  Mesentery. 

a,  Bundles  of  fibrous  tissue ;   6,  networks  of  elastic 
fibres.     (.Atlas.) 


When 


44  Elements  of  Histology.  [Chap.  v. 

connected  into  networks  within  the  bundle,  are  to  be 
specially  found  in  considerable  numbers  in  the  walls 
of  the  alveoli  of  the  lung,  in  the  ligamenta  flava,  in 
the  ligamentum  nuchse  of  the  ox — in  which  the  fibres 
are  exceedingly  thick  cylinders, — in  yellow  elastic  car- 
tilage (see  below),  in  the  endocardium  and  valves  of 
the  heart,  and  in  the  vascular  system,  particularly  the 
arterial  division.  In  the  latter  organs  the  intima, 
and  also  to  a  great  extent  the  media,  consist  of  elastic 
fibrils  densely  connected  into  a  network. 

52.  The  following  are  special  morphological  modi- 
fications of  the  elastic  fibres  :  (a)  elastic  fenestrated 
membranes  of  Henle,  as  met  with  in  the  intima 
of  the  big  arteries;  these  are  in  reality  ^  networks 
of  fibres  with  very  small  meshes,  and  the  fibres 
unusually  broad  and  flat,  (b)  Homogeneous  elastic 
membranes,  which  surround,  as  a  delicate  sheath,  the 
connective  tissue  trabecular  in  some  localities,  e.g., 
subcutaneous  tissue,  (c)  Homogeneous-looking  elastic 
membranes  in  the  cornea,  found  behind  the  anterior 
epithelium  as  Bowman's  elastica  anterior,  and  at  the 
back  of  the  cornea  as  elastica  posterior,  or  Descemet's 
membrane;  in  this  latter  bundles  of  minute  fibrils 
have  been  observed,  (d)  Elastic  trabecular  forming  a 
network,  as  in  the  ligamentum  pectinatum  iridis. 
In  the  embryonal  state  the  elastic  fibres  are  nucleated, 
the  nuclei  being  the  last  remnants  of  the  cells  from 
which  the  fibres  develop — one  cell  generally  giving 
origin  to  one  fibre.  Such  nucleated  fibres  are  called 
Henle's  nucleated  fibres. 

53.  Special  varieties  of  fibrous  connective  tissue 
are  these  : — 

(1)  Adenoid  retiadum.  This  is  a  network  of  fine 
fibrils,  or  plates,  forming  the  matrix  of  lymphatic  or 
adenoid  tissue  (see  Lymphatic  Glands).  The  reticulum 
is  not  fibrous  connective  tissue  nor  elastic  tissue  ;  it 
contains  nuclei  in  the  young  state,  being  derived  from 


Chap,  vi.]  Cartilage.  45 

a  network  of  branched  cells ;  but  in  the  adult  state 
the  reticulum  itself  possesses  no  nuclei.  Those  found  on 
it  do  not  form  an  essential  part  of  it. 

(2)  The  neuroglia  of  Virchow  is  a  dense  network 
of  very  fine  homogeneous  fibrils  forming  the  support- 
ing tissue  for  the  nervous  elements  in  the  central 
nervous  system.  These  fibrils  are  supposed  to  be 
elastic  fibres  (Gerlach).  Embedded  in  the  network  of 
these  fibres  are  found  branched  nucleated  flattened 
cell  plates,  which  are  the  proper  connective  tissue  cells. 

(3)  Gelatinous  tissue.  This  occurs  chiefly  in 
the  embryo,  being  the  unripe  state  of  fibrous 
connective  tissue.  It  consists  of  spindle-shaped  or 
branched  connective  tissue  cells,  separated  from  one 
another  by  a  homogeneous  transparent  mucoid  sub- 
stance. It  is  met  with  in  the  umbilical  cord  of  the 
embryo,  and  in  the  places  where  fibrous  connective 
tissue  is  to  be  developed.  After  birth  it  is  found  in 
the  tissue  of  the  pulp  of  the  teeth,  and  in  the  cavity 
of  the  middle  ear,  and  in  some  places  as  precursor 
of  fat  tissue. 


CHAPTER  VI. 

CARTILAGE. 

54.  Cartilage  consists  of  a  firm  ground  substance 
which  yields  chondrin,  and  of  cells  embedded  in  it. 
Most  cartilages  (except  on  the  articulation  surface) 
are  covered  on  their  free  surface  with  a  membrane  of 
fibrous  connective  tissue  with  a  few  elastic  fibrils. 
This  membrane  is  supplied  with  blood-vessels,  lym- 
phatics, and  nerves,  and  is  of  essential  importance  for 
the  life  and  growth  of  the  cartilage.  This  is  the  peri- 
chondrium.     There  are  three  varieties  of  cartilage. 


46 


Elements  of  Histology. 


[Chap.  vi. 


55.  (1)  Hyaline  cartilage  (Fig.  30a).  This  occurs 
at  the  articular  surfaces  of  all  bones ;  on  the  borders 
of  many  short  bones ;  at  the  sternal  part  of  the  ribs, 
as  costal  cartilages ;  at  the  margin  of  the  sternum, 
scapula,  and  os  ileum ;  in  the  rings  of  the  trachea,  the 
cartilages  of  the  bronchi,  the  septum  and  lateral  carti- 
lages of  the  nose  ;  and  in 
the  thyroid  and  cricoid 
cartilages  of  the  larynx. 
The  ground  substance  is 
hyaline,  transparent, 
ground  -  glass  -  like,  and 
firm.  The  cells  are 
spherical  or  oval  proto- 
plasmic corpuscles,  each 
with  one  or  two  nuclei. 
They  undergo  division, 
and  although  the  two  off- 
spring are  at  first  close 
together — half-moon-like 
— they  gradually  grow  wider  apart  by  the  deposit 
of  hyaline  ground  substance  between  them.  The 
cells  are  contained  in  special  cavities  called  the 
cartilage  lacunas.  Each  cell  generally  occupies  one 
lacuna,  but  according  to  the  state  of  division  a  lacuna 
may  contain  two,  four,  six,  or  eight  cartilage  cells ; 
the  latter  are  those  cases  in  which  division  proceeds 
at  a  more  rapid  rate  than  the  deposition  or  formation 
of  hyaline  ground  substance  between  the  cells. 

The  part  of  the  cartilage  next  to  the  perichondrium 
shows  most  active  growth ;  hence  the  cells  are  here  smaller, 
closer  together,  and  there  is  less  ground  substance. 

Each  lacuna  is  limited  by  a  delicate  membrane, 
and,  according  to  the  state  of  the  cell,  is  either  com- 
pletely or  partially  filled  out  by  it.  This  membrane 
is  called  the  capsule  (Fig.  30a).  In  many  cartilages, 
especially  in  growing  cartilage,  it  is  thickened  by  the  ad- 


Fig.  30a.  —  Hyaline    Cartilage   of 
Human  Trachea. 

In  the  hyaline  ground  substance  are 
seen  the  cartilage  cells  enclosed  in 
capsules. 


Chap.  VI.] 


Cartilage. 


47 


Fig.    30b. 


dition  of  a  layer  or  layers  of  hyaline  ground  substance  ; 
this  is  the  most  recently-formed  part  of  the  matrix,  but 
is  still  distinct 
from  the  rest  of 
the  ground  sub- 
stance. 

56.  In  some 
places,  especi- 
ally in  articular 
cartilage  (Till- 
manns,  Baber), 
bundles  of  fine 
conne  ctive 
tissue  fibrils 
may  be  noticed 
in  the  hyaline 
ground  sub- 
stance. 

57.  In  some 
cartilages,     the 

protoplasm  of  the  cell  becomes  filled  with  fat  globules 
(Fig.  30c).  This  fact  may  be  observed  in  many  normal 
cartilages ;  sometimes  the  fat  globules 
become  confluent  into  one  large  drop, 
and  then  the  cell  has  the  appearance  of 
a  fat  cell.  In  age,  disease,  and  defi- 
cient nutrition,  lime  salts  are  deposited 
in  the  ground  substance,  beginning 
from  the  circumference  of  the  cells. 
The  lime  matter  appears  in  the  shape 
of  opaque  granules,  or  irregular  or 
angular  clumps.  The  ground  sub- 
stance thereby  loses  its  transparency, 
becomes  opaque  in  transmitted,  white 
in  reflected,  light,  and,  of  course,  very 
hard  and  brittle.  This  process  is  the  calcification  of 
cartilage.    It  is  also  met  with  in  cartilage  that  is  to  be 


From    a    Preparation   of    Sternal 
Cartilage  of  Newt. 

The  lacunas,  containing  the  cartilage  cells,  anastomose 
by  fine  channels. 


Fig.  30C— Three  Car- 
tilage Cells  filled 
with  Fat  Droplets. 
From  the  hyaline 
cartilage  of  the 
nasal  septum  of 
Guinea-pig. 


48  Elements  of  Histology.         [Chap.  vi. 

replaced  by  bone,  being  the  precursor  of  the  formation 
of  bone,  as  in  the  embryo  {see  below),  and  at  the 
growing  ends  of  tubular  bones. 

58.  The  multiplication  of  the  cartilage  cells  has 
been  observed  during  life  by  Schleicher  and  Flemming. 
It  takes  place  after  the  mode  of  karyokinesis.  The 
lacunae  of  the  cartilage  are  not  isolated  cavities,  but 
are  connected  with  one  another  by  fine  channels  (Fig. 
30b),  so  that  the  ground  substance  is  easily  permeable 
by  the  current  of  nutritive  fluid.  These  channels  and 
lacunae  make  one  intercommunicating  system,  and  are 
connected  with  the  lymphatics  of  the  perichondrium 
(Budge).  Formed  matter — like  pigment  granules,  red 
and  white  blood  corpuscles,  and  pus  corpuscles — may 
also  find  its  way  into  the  channels  and  lacunae  of  the 
cartilage  from  the  perichondrium. 

At  the  borders  of  articular  cartilage,  where  it  is 
joined  to  the  synovial  membrane  and  the  articulation- 
capsule,  the  cartilage  cells  are  more  or  less  branched, 
and  pass  insensibly  into  the  branched  connective  tissue 
cells  of  the  membrane.  In  foetal  hyaline  cartilage 
many  of  the  cells  are  spindle-shaped  or  branched. 

59.  In  the  cartilage  separating  the  bone  of  the 
apophyses  from  the  end  of  the  diaphysis  of  tubular 
bones,  there  is  a  peculiar  hyaline  cartilage,  known  as 
the  intermediary  or  ossifying.  Its  cells  are  arranged  in 
characteristic  vertical  rows,  owing  to  the  continued 
division  of  the  cells  in  a  transverse  direction. 

Cartilages,  or  parts  of  cartilages,  in  which  the  cells 
are  very  closely  placed,  owing  to  the  absence,  or  im- 
perfect deposit  and  formation,  of  ground  substance, 
are  called  parenchymatous. 

60.  (2)  Fitoro-cartilage,  or  connective  tissue 
cartilage,  occurs  as  the  intervertebral  discs,  as  the 
interarticular  cartilages,  sesamoid  cartilages,  and  as 
that  forming  the  margin  of  a  fossa  glenoidalis.     It  is 

fibrous  connective  tissue  arranged  in  bundles,  and  these 


Chap.  VI.] 


Cartilage. 


49 


again  in  layers.  The  ground  substance  of  this  carti- 
lage is  said  (?)  to 
yield  chondrin  and 
not  glutin.  Be- 
tween the  strata  of 
the  fibrous  bundles 
are  rows  of  more  or 
less  flattened  oval 
protoplasmic  nu- 
cleated cells,  each 
invested  in  a  deli- 
cate capsule(Fig.  31). 
They  are  less  flat- 
tened than  the  cells 
of  tendon,  and  the 
capsule  distinguishes 
the  two.  Where  fibro- 
cartilage  passes  into 
tendinous     tissue, 

the  two  kinds  of  cells  pass  insensibly  into  one  another. 

61.  (3)  Yellow,  or 
elastic  cartilage. — 
This  variety  is  also  called 
reticular  ;  it  occurs  in  the 
epiglottis,  in  the  ear-lobe, 
in  the  Eustachian  tube,  in 
the  cartilages  of  Wris- 
berg  and  Santorini  in  the 
larynx.  In  the  early 
stage  this  kind  is  hyaline. 
Gradually  numbers  of 
elastic  fibrils  make  their 
appearance,  growing  into 
the  cartilage  matrix  from 
the  perichondrium  in  a 
more  or  less  vertical  direc- 
anastomosing    with    one 


Fig.  31.— Fibro-Cartilage  of  an  Interver- 
tebral Ligament. 

Showing  the  bundles  of  fibrous  tissue  and  rows 
of  cartilage  cells.    (Atlas.) 


i-a 


Fig.  32.— From  a  Section  through 
the  Epiglottis. 

«,  Perichondrium ;  b,  networks  of 
elastic  fibrils  surrounding  the  carti- 
lage cells.    (Atlas.) 


tion,    and    branching    and 


50  Elements  of  Histology.        [Chap.  vn. 

another.  The  final  stage  is  reached  when  the  ground 
substance  is  permeated  by  dense  networks  of  elastic 
fibrils  (Fig.  32),  so  arranged  that  spherical  or  oblong 
spaces  are  left,  each  of  which  contains  one  or  two 
cartilage  cells,  surrounded  by  a  smaller  or  larger  zone 
of  hyaline  cartilage  ground  substance. 


CHAPTER    VII. 

BONE. 

62.  Bone,  or  osseous  substance,  is  associated  with 
several  other  soft  tissues  to  form  an  anatomical 
individual. 

(a)  The  periosteum.— Except  at  the  articular 
surfaces,  and  where  bones  are  joined  with  one  another 
by  ligaments  or  cartilage,  all  bones  are  covered  with  a 
vascular  membrane  of  fibrous  connective  tissue.  This 
is  the  periosteum.  It  consists  in  most  instances  of 
an  outer  fibrous  layer,  composed  of  bundles  of  fibrous 
tissue  densely  aggregated,  and  an  inner,  or  osteogenetic 
layer,  which  is  of  loose  texture,  consisting  of  a  mesh- 
work  of  thin  bundles  of  fibrous  tissue,  in  which 
numerous  blood-vessels  and  many  protoplasmic  cells  are 
contained.  The  blood-vessels  form  by  their  capillaries 
a  network.  The  cells  are  spheroidal  or  oblong,  each 
with  one  spherical  or  oval  nucleus.  They  have  to 
form  bone-substance,  and  are  therefore  called  the  osteo- 
blasts (Gegenbaur). 

(b)  The  cartilage  is  hyaline  cartilage,  and  its 
distribution  on  and  connection  with  bone  have  been 
mentioned  in  §§  55  and  59. 

G3.  (c)  The  marrow  of  bone  is  a  vascular  soft 
tissue,  filling  up  all  spaces  and  cavities.     It  consists 


chap,  vii.]  Bone.  51 

of  a  small  amount  of  fibrous  tissue  as  a  matrix,  and 
in  it  are  embedded  numerous  blood-vessels  and  cells. 
The  few  afferent  arterioles  break  up  into  a  dense  net- 
work of  capillaries,  and  these  are  continued  as  plexuses 
of  veins,  characterised,  by  their  size  and  exceedingly 
thin  walls.  The  cells  are  of  the  same  size,  aspect,  and 
shape  as  the  osteoblasts  of  the  osteogenetic  tissue,  and 
they  are  called  marrow  cells. 

In  origin  and  structure,  the  tissue  of  the  osteo- 
genetic layer  of  the  periosteum  and  the  marrow  are 
identical.  In  the  embryo,  the  marrow  is  derived 
from  an  ingrowth  of  the  osteogenetic  layer  of  the 
periosteum  (see  below),  and  also  in  the  adult  the  two 
tissues  remain  directly  continuous.  As  will  be  shown 
later,  the  marrow  at  the  growing  ends  of  the  bones 
is  concerned  in  the  new  formation  of  osseous  substance 
in  the  same  way  as  the  osteogenetic  layer  of  the  peri- 
osteum is  in  that  of  the  surface ;  and  in  both  tissues 
the  highly  vascular  condition  and  the  cells  (osteoblasts 
of  the  osteogenetic  layer,  and  marrow  cells  of  the 
marrow)  are  the  important  elements  in  this  bone 
formation.  Marrow  is  of  two  kinds,  according  to 
the  condition  of  the  cells.  If  many  or  most  of  these 
are  transformed  into  fat  cells,  it  has  a  yellowish  aspect, 
and  is  called  yellow  marrow  ;  if  few  or  none  of  them 
have  undergone  this  change,  it  looks  red,  and  is  called 
red  marrow.  In  the  central,  or  marrow,  cavity  of  the 
shaft  of  tubular  bones,  and  in  the  spaces  of  some 
spongy  bones,  the  marrow  is  yellow ;  at  the  ends  of  the 
shaft,  in  the  spongy  bone  substance  in  general,  and  in 
young  growing  bones,  it  is  red. 

The  cells,  especially  those  of  red  marrow,  are  the 
elements  from  which  normally  vast  numbers  of  red 
blood-corpuscles  are  formed,  as  has  been  mentioned  on 
a  former  page. 

In  marrow,  particularly  in  red  marrow,  we  meet 
with  huge  multinucleated  cells,  called  Myeloplaxes  of 


52 


Elements  of  Histology. 


[Chap.  VII. 


Robin.  They  are  derived  by  overgrowth  from  ordinary 
marrow  cells,  and  are  of  importance  for  the  absorption 
and  formation  of  bone  {see  below).  According  to 
Heitzmann,  Malassez,  and  others,  they  also  have  to 
do  with  the  formation  of  blood-vessels  and  blood- 
corpuscles. 

64.  The  matrix  of  osseous  substance  is  dense 
fibrous  connective  tissue,  i.e.,  a  tissue  yielding  gelatin 
on  boiling.  The  cement  substance  between  the  fibrils 
is  petrified,  owing  to  a  deposit  of  insoluble  inorganic 
lime  salts,  chiefly  carbonates  and  phosphates.  These 
can  be  dissolved  out  by  strong  acids  (hydrochloric) 
and  are  thereby  converted  into  soluble  salts.  Thus 
the  organic  matrix  of  osseous  substance — called  ossein 
— may  be  obtained  as  a  soft  flexible  material,  easily 
cut. 

The  bone  substance  is  in  the  adult  state'  generally 
lamellated,  the  lamellse  being  of  microscopic  thinness. 

Between  every  two 
lamellae  are  num- 
bers of  isolated, 
flattened,  oblong 
spaces — the  bone 
lacunce  (Fig.  33), 
which  anastomose 
by  numerous  fine 
canals  with  one 
another,  and  also 
with  those  of  the 

Fig.  33.— Osseous  Lamellae ;  oblong  branched      next  lamella  above 

jAtitfeCUB8eaildcanaliCulibetweentliein*     and    below.      The 

appearances  are 
very  similar  to  those  presented  by  the  lacuna?  and 
canaliculi  containing  the  corneal  corpuscles,  as  des- 
cribed in  Chapter  V. 

These  bone  lacunae  and  their  canaliculi  are  the  lymph- 
canalicular  system  of  osseous  substance,  for  they  are 


chap,  vii.]  Bone.  53 

in    open    and    free    communication    with    lymphatic 
vessels  of  the  marrow  spaces  and  Haversian  canals. 

65.  In  the  bone  matrix,  each  lacuna  contains  also 
a  nucleated  protoplasmic  cell,  called  the  bone  cell,  which, 
however,  does  not  fill  it  completely.  In  the  young 
state,  the  cell  is  branched,  the  branches  passing  into 
the  canaliculi  of  the  lacunae ;  but  in  the  old  state  very 
few  processes  can  be  detected  on  a  bone  cell,  which, 
with  its  lacuna  and  canaliculi,  is  called  a  bone  cor- 
puscle. 

66.  According  to  the  arrangement  of  the  bone 
substance,  we  distinguish  compact  from  spongy  sub- 
stance. The  former  occurs  in  the  shaft  of  tubular 
bones  and  in  the  outer  layer  of  flat  and  short  bones. 
Its  lamellae  are  arranged  as :  (a)  concentric  or  Haversian 
lamella?,  directly  surrounding  the  Haversian  canals 
(Fig.  33a).  These  are  fine  canals  of  varying  lengths 
pervading  the  compact  substance  in  a  longitudinal  direc- 
tion, and  anastomosing  with  one  another  by  transverse 
or  oblique  branches.  The  Haversian  canals  near  the 
marrow  cavity  are  larger  than  those  near  the  perios- 
teum. As  a  matter  of  fact,  those  next  to  the  marrow 
cavity  become  gradually  enlarged  by  absorption,  until 
finally  they  are  fused  with  the  marrow  cavity.  Each 
Haversian  canal  contains  a  blood-vessel,  one  or  two 
lymphatics,  and  a  variable  amount  of  marrow  tissue. 
These  canals  open  both  into  the  marrow  cavity  and  on 
the  outer  surface  into  the  osteogenetic  layer  of  the  peri- 
osteum, and  they  form  the  means  by  which  the  latter 
remains  in  continuity  with  the  marrow.  They  are 
surrounded  by  numbers  of  concentric  bone  lamella?, 
with  the  bone  corpuscles  between  them,  and  this  is  a 
system  of  concentric  lamella?.  Near  the  external  sur- 
face of  the  compact  substance  the  number  of  lamellae 
in  each  system  is  smaller  than  in  the  deeper  parts. 
(6)  Between  these  systems  of  concentric  lamellae  are 
the  interstitial  or  ground  lamellos;  they  run  in  various 


54 


Elements  of  Histology.        [Chap.  vii. 


directions,  and  in  reality  fill  the  interstices  between 
the  systems  of  the  Haversian  or  concentric  lamellae. 
Near  the  external  surface  of  long  bones  they  have  pre- 
eminently a  direction  parallel  to  the  surface.  These  are 
the  circumferential  lamellae  of  Tomes  and  de  Morgan. 


Fig.  33a. — Compact  Bone  fouosiance  in  Cross  Section. 

a,  Concentric  lamellae  arranged  around  the  Haversian  canals,  cut  across ; 
b,  interstitial  or  ground  lamella?.  The  bone  lacunas  are  seen  between  the 
bone  lamella?.    (Atlas.) 

The  lamellaB  of  compact  bone  are  perforated  by  per- 
pendicular petrified  fibres,  the  perforating  fibres  of 
Sharpey.  They  form  a  continuity  with  the  fibres  of 
the  periosteum,  from  which  they  are  developed. 

Some  of  these  fibres  are  fine,  and  of  the  nature  of 
elastic  fibres. 

67.  Spongy  bone  substance  occurs  in  the  end  of  the 
shaft,  in  the  apophyses,  in  short  bones,  and  in  the 
diploe  of  flat  bones.  The  cavities  or  meshes  of  the 
spongy  substance  are  called  Haversian  spaces ;  they 
intercommunicate  with  one  another,  and  are  filled 
with  marrow,  which  in  the  young  and  growing  state 
is  generally  of  the  red  variety.  The  firm  parts  are  of 
the  shape  of  spicules  and  septa,  called  bone  trabeculce, 


Chap,  vii.]  Bone.  55 

of  varying  length  and  thickness,  and  are  composed  of 
lamellae  of  bone  substance. 

According  to  the  arrangement  of  the  trabecule, 
the  spongy  substance  is  a  uniform  honey-combed  sub- 
stance, or  appears  longitudinally  striated,  as  in  the 
end  of  the  shaft.  In  the  latter  case  the  marrow  spaces 
are  elongated  and  the  trabecule  more  or  less  parallel,  but 
anastomosing  with  one  another  by  transverse  branches. 

68.  Development  of  bone. — Bone  is  developed 
in  the  embryo,  and  continues  to  be  formed  also  after 
birth  as  long  as  bone  grows,  either  in  the  cartilage,  or 
independently  of  this  directly  from  the  osteogenetic 
layer  of  the  periosteum.  The  former  mode  is  called 
endochondral,  the  latter  periosteal,  or  intermembranous 
formation. 

All  bones  of  the  limbs  and  of  the  vertebral 
column,  the  sternum,  and  the  ribs,  and  the  bones 
forming  the  base  of  the  skull,  are  preformed  in  the 
early  embryo  as  solid  hyaline  cartilage,  covered  with  a 
membrane  identical  in  structure  and  function  with 
the  periosteum,  which  at  a  later  period  it  becomes.  The 
tegmental  bones  of  the  skull,  the  bones  of  the  face, 
the  lower  jaw,  except  the  angle,  are  not  preformed  at 
all,  only  a  membrane  identical  with  the  future  perios- 
teum being  present,  and  underneath  and  from  it  the 
bone  is  gradually  being  deposited. 

69.  Endochondral  formation.  —  The  stage 
next  to  the  one  (1)  in  which  we  have  solid  hyaline 
cartilage  covered  with  periosteum  is  the  following 
(2)  :  Starting  from  the  "  centre,  or  point,  of  ossifica- 
tion," and  proceeding  in  all  directions,  the  cartilage 
becomes  permeated  by  numbers  of  channels  (cartilage 
channels)  containing  prolongations  (periosteal  processes 
of  Yirchow)  of  the  osteogenetic  layer  of  the  periosteum, 
i.e.,  vessels  and  osteoblasts,  or  marrow  cells.  This  is 
the  stage  of  the  vascularisation  of  the  cartilage.  In 
the  next  stage  (3)  the  cartilage  bordering  on  these 


56 


Elements  of  Histology.        [chap.  vn. 


channels  grows  more  transparent,  the  lacunae  becoming 

enlarged  and  the 
cartilage  cells  more 
transparent.  The  lat- 
ter gradually  break 
down,  while  the  in- 
tercellulartrabeculse 
become  calcified; 
the  lacunae  them- 
selves, by  absorp- 
tion, fusing  with  the 
cartilage  channels. 
These  latter  there- 
by become  trans- 
formed into  irregu- 
lar cavities,  which 
are  bordered  by,  and 
into  which  project, 
trabeculm  of  calcified 
cartilage.  The  cavi- 
ties are  the  primary 
marrow  cavities,  and 
they  are  filled  with 
the  primary  or  car- 
tilage marrow,  i.e., 
blood  -  vessels  and 
osteoblasts,  derived, 
as  stated  above,  from 
the  osteogenetic 
layer  of  the  perios- 
teum. (4)  The  os- 
teoblasts arrange 
themselves  by  active 
multiplication  as  an 
epitheloid  layer  on 
the  surface    of   the 

calcified  cartilage  trabeculae  projecting  into,  and  bor- 


Fig.  34.—  Longitudinal  Section  through  the 
entire  Foetal  Humerus  of  a  Guinea-pig. 

a,  Periosteum  ;  5,  hyaline  cartilage  of  the  epiphysis ; 

c,  intermediate  cartilage  at  the  end  of  the  shaft ; 

d,  zone  of  cal  ciflcation ;  e,  periosteal  bone, spongy ; 
/,  endochondral  bone,  spongy. 


chap,  vii.]  Bone.  57 

dering  the  primary  marrow  cavities.  The  osteoblasts 
form  bone  substance,  and  as  this  proceeds,  the  calcified 
cartilage  trabecular  become  gradually  ensheathed  and 
covered  with  a  layer  of  osseous  substance, — the  osseous 
matrix  and  branched  bone  corpuscles.  Thus  the 
original  cartilage  gradually  assumes  the  appear- 
ance of  a  spongy  substance,  in  which  the  cavities 
(primary  marrow  cavities)  are  filled  with  the  primary 
marrow,  and  are  of  considerable  size,  while  the 
trabecule  bordering  them  are  calcified  cartilage 
covered  with  layers  of  new  bone.  The  marrow  cells, 
or  osteoblasts,  continue  to  deposit  bone  substance  on 
the  free  surface  of  the  trabecule,  while  the  calcified 
cartilage  in  the  centre  of  the  trabecular  gradually 
becomes  absorbed. 

70.  The  nearer  the  centre  of  ossification,  the 
more  advanced  the  process,  i.e.,  the  more  bone  the 
less  calcified  cartilage  is  found  in  the  trabecular, 
and  the  thicker  the  latter.  At  the  "centre  of  ossifi- 
cation," i.e.,  whence  it  started,  the  process  is  further 
advanced ;  away  from  it,  it  is  in  an  earlier  stage. 
At  this  period  of  embryo  life,  between  the  centre  of 
ossification  and  a  point  nearer  to  the  extremity  of 
the  shaft  of  a  tubular  bone,  all  stages  described  above 
may  be  met  with,  viz.,  between  the  solid  unaltered 
hyaline  cartilage  at  the  end  of  the  shaft,  and  the 
spongy  bone  with  the  unabsorbed  remains  of  calcified 
cartilage  in  the  middle  of  the  shaft,  all  intermediate 
stages  occur  (Fig.  34). 

71.  After  birth,  and  as  long  as  bone  grows,  we 
find  in  the  end  of  the  shaft,  and  to  a  further  degree 
also  in  the  epiphysis,  a  continuation  of  the  above 
process  of  endochondral  formation.  In  fact,  all 
bones  preformed  in  the  embryo  as  cartilage  grow  in 
length  before  and  after  birth  by  endochondral  formation 
of  new  bone.  The  hyaline  cartilage  at  their  ex- 
tremities (intermediate  or  ossifying  cartilage)  is  the 


53 


Elements  of  Histology. 


[Chap.  VII. 


cartilage  at  the  expense  of  which  the  new  bone  is 
formed,  by  the  marrow  (blood-vessels  and  marrow- 
cells  or  osteoblasts)  of  the  spongy  substance  in  con- 


tact with  the  cartilage. 


72.  Following  the  development  of  a  tubular  bone 
after  the  above-mentioned  stage  4,  we  find  that  the 
spongy  bone  once  formed  is  not  a  permanent  structure, 


Fig.  35.— From  a  Transverse  Section  through  the  Tibia  of  Foetal  Kitten. 

a,  Fibrous  layer  of  the  periosteum ;  b  osteogenetic  layer  of  the  periosteum  ; 
c,  periosteal  bone:  a,  calcined  cartilage  not  covered  yet  by  bone;  below  this 
layer  the  trabecules  of  calcified  cartilage  covered  with  plates  of  bone- 
shaded  darkly  in  the  figure  ;  e,  boundary  between  periosteal  and  endochondral 
bone.    (Atlas.) 


Chap,  vii.]  Bone.  59 

but  becomes  gradually  absorbed  altogether,  and  this 
process  also  starts  from  the  points  of  ossification.  Thus 
a  continuous  cavity  filled  with  marrow  is  formed,  and 
this  first  appears  in  the  region  of  the  centre  of  ossifi- 
cation, and  represents  the  rudiment  of  the  future 
continuous  central  marrow  cavity  of  the  shaft.  Simul- 
taneously with  or  somewhat  previous  to  this  absorp- 
tion of  the  endochondral  bone,  new  bone — spongy 
bone — is  deposited  directly  by  the  osteogenetic  layer 
of  the  periosteum  on  the  outer  surface  of  the  en- 
dochondral bone.  This  also  commences  at  the  centre  of 
ossification  and  proceeds  from  here  gradually  to  further 
points.  This  is  the  periosteal  bone  (Figs.  34,  35).  It  is 
formed  without  the  intervention  of  cartilage  directly 
by  the  osteoblasts  of  the  osteogenetic  layer.  And  as 
fresh  layers  of  osteoblasts  by  multiplication  appear  on 
the  surface  of  the  periosteal  bone,  new  layers  of  bone 
trabecule  are  formed,  and  also  the  old  trabeculae  become 
increased  in  thickness.  In  the  meshes  or  Haversian 
spaces  of  this  spongy  periosteal  bone  the  same  tissue 
is  of  course  to  be  found  as  constitutes  the  osteo- 
genetic layer  of  the  periosteum,  being  derived  from 
and  continuous  with  it. 

In  these  Haversian  spaces  concentric  lamellae  of 
bone  substance  become  formed  by  the  osteoblasts,  and 
spongy  is  thus  transformed  into  compact  bone,  while 
at  the  same  time  the  Haversian  spaces,  being  nar- 
rowed in  by  the  deposit  in  them  of  the  concentric 
lamellae,  are  transformed  into  the  Haversian  canals. 
When  this  compact  bone  is  again  absorbed — e.g.,  that 
next  the  central  marrow  cavity  of  the  shaft  of  a 
tubular  bone — the  concentric  lamellae  are  first  ab- 
sorbed, the  Haversian  canal  being  in  this  way  again 
transformed  into  a  Haversian  space. 

73.  At  birth  all  the  primary  endochondral  bone  has 
already  disappeared  by  absorption  from  the  centre  of 
the  shaft,  while  the  bone  present  is  all  of  periosteal 


6o 


Elements  of  Histology.        [Chap.  vn. 


C^).-lH?- 


C?s^  : -*&)-;< *?iJ -' 


<g> 


^6J 


origin.     At  the  extremity  of  the  shaft,  however,  the 

spongy  bone  is  all 
endochondral  bone, 
and  it  continues  to 
grow  into  the  inter- 
mediate cartilage  as 
stated  above,  as  long 
as  the  bone  as  a  whole 
grows  (Fig.  36). 
Of  course  the  parts 
of  this  spongy  bone 
nearest  to  the  centre 
of  the  shaft  are  the 
oldest,  and  ulti- 
mately disappear  by 
absorption  into  the 
central  marrow 
cavity.  In  the  epi- 
physis the  spongy 
bone  is  also  endo- 
chondral bone,  and 
its  formation  is  con- 
nected with  the  deep 
layer  of  the  articu- 
lar cartilage. 

Underneath  the 
periosteum  and  on 
the  surface  of  the 
spongy  endochon- 
dral bone  at  the 
extremity  of  the 
shaft,  the  periosteal 
bone  is  represented 
only  as  a  thin  layer, 
extending  as  far 
the  margin  of  the 


Fig.  36. — From  a  Longitudinal  Section  of 
Femur  of  Eabbit,  through  the  part  in 
which  the  intermediary  cartilage  joins 
the  end  of  the  shaft. 

a.  Intermediary  cartilage;  6,  zone  of  calcified 
cartilage;  c,  zone,  in  which  the  calcified 
trabeculae  of  cartilage  become  gradually  in- 
vested in  osseous  substance,  shaded  light  in 
the  figure ;  the  spaces  between  the  trabeculae 
contain  marrow,  and  the  capillary  blood- 
vessels are  seen  here  to  end  in  loops;  d,  in 
this  zone  there  is  more  bone  formed  :  the 
greater  amount  the  farther  away  from  this 
zone.    (Atlas.) 


as  the  periosteum  reaches,  e.g.,  to 
articular  cartilage. 


Chap.  VII.] 


Bone. 


61 


74.  Intermembranons    formation. — All 

bones  not  preformed  in  the  embryo  as  cartilage  are 
developed  directly  from  the  periosteum  in  the  manner 
of  the  periosteal  bone  just  described  (Fig.  37).    Here  also 


Fig.  37. — A  small  mass  of  Bone  Substance  in  the  Periosteum  of  the 
Lower  Jaw  of  a  Human  Foetus. 

a,  Osteogenetic  layer  of  periosteum  ;  6,  multinucleated  giant  cells,  myeloplaxes. 
The  one  in  the  middle  of  the  upper  margin  corresponds  to  an  osteoclast, 
whereas  the  smaller  one  at  the  left  upper  corner  appears  concerned  in  the 
formation  of  hone.  Above  c  the  osteoblast  cells  become  surrounded  by 
osseous  substance  and  thus  become  converted  into  bone-cells.    (Atlas.) 


the  new  bone  is  at  first  spongy  bone,  which  in  its  inner 
layers  gradually  becomes  converted  into  compact  bone. 

In  all  instances  during  embryo  life  and  after 
birth  the  growth  of  a  bone  in  thickness  takes  place 
after  the  manner  of  'periosteal  hone ;  this  is  at  first 
spongy,  but  is  gradually  converted  into  compact  bone. 

75.  All  osseous  substance  is  formed  in  the  embryo 
and  after  birth  by  the  osteoblast  or  marrow  cells 
(Gegenbaur,  Waldeyer)  :  each  osteoblast  giving  origin 
to  a  zone  of  osseous  matrix,  and  in  the  centre  of  this 


62  Elements  of  Histology.        [Chap.  vn. 

to  a  nucleated  protoplasmic  remnant,  which  gradually 
becomes  branched  and  then  represents  a  bone  cell. 
The  osseous  matrix  is  at  first  a  soft  fibrillar  tissue, 
but  is  gradually  and  uniformly  impregnated  with 
lime  salts.  This  impregnation  always  starts  from  the 
centre  of  ossification. 

76.  Wherever  absorption  of  calcified  cartilage  or  of 
osseous  substance  is  going  on,  we  meet  with  the  multi- 
nucleated huge  protoplasmic  cells,  called  the  myelo- 
plaxes  of  Robin.  Kolliker  showed  them  to  be  impor- 
tant for  the  absorption  of  bone  matrix,  and  called 
them  therefore  Osteoclasts  (Fig.  37).  For  cartilage  they 
may  be  called  Chondroclasts.  When  concerned  in  the 
absorption  we  find  these  myeloplaxes  situated  in 
smaller  or  larger  pits,  which  seem  to  have  been  pro- 
duced by  them  ;  these  absorption  pits  or  lacunae  on  the 
surface  of  bones  are  called  Howship's  lacunae.  They 
invariably  contain  numbers  of  osteoclasts.  It  can, 
however,  be  shown  that  myeloplaxes  are  also  con- 
cerned in  the  formation  of  bone,  by  giving  origin  to  a 
number  of  new  osseous  zones  with  their  bone  cells. 
In  the  earliest  stages  of  development  of  the  foetal  jaw 
this  process  is  seen  with  great  distinctness  (Fig.  37). 

77.  Dentine  forms  the  chief  part  of  a  tooth.  It 
consists  of  a  petrified  matrix,  in  which  are  numbers  of 
perpendicularly-arranged  canals — the  dentinal  tubes — 
containing  the  dentinal  fibres.  It  is  in  some  respects 
similar  to  bone,  although  differing  from  it  in  certain 
essentials.  It  is  similar,  inasmuch  as  it  is  developed 
in  like  manner  by  some  peculiarly  transformed 
embryonal  connective  tissue — viz.,  by  the  tissue  of  the 
embryo  tooth  papilla — and  inasmuch  as  cells  are  con- 
cerned in  the  production  both  of  the  petrified  matrix 
(impregnated  with  lime  salts),  and  of  the  processes  of 
the  cells  contained  in  its  canals — the  dentine  fibres. 
The  details  of  structure  and  distribution  will  be 
described  in  connection  with  the  teeth. 


Chap.  VIII.] 


63 


CHAPTER  VIII. 

NON-STRIPED    MUSCULAR    TISSUE. 

78.  This  tissue  consists  of  nucleated  cells,  which, 
unlike  amoeboid  cells,  are  contractile  in  one  definite 
direction,  becoming  shorter  and  thicker  during  con- 
traction. 

The  cells  are  elongated,  spindle-shaped,  or  band-like 
(Fig.  38a),  and  drawn  out  at  each  extremity  into  a  longer 
or  shorter,  generally  single  but  occasionally  branched, 
tapering  process.     Each  cell  includes  an  oval  nucleus. 


Fig.  38a. — Non-striped  Muscular  Fibres,  isolated. 

The  cross-markings  indicate  corrugations  of  the  elastic  sheath  of  the  individual 
fibres.    (Atlas.) 


which  is  flattened  if  the  cell  it  belongs  to  is  flattened. 
The  cell-substance  is  a  pale  homogeneous-looking  or 
finally  and  longitudinally  striated  substance. 

During  extreme  contraction  the  nucleus  may 
become  more  or  less  plicated,  so  that  its  outline  be- 
comes wavy  or  zig-zag. 

It  has  been  shown  (Klein)  in  certain  preparations — 
e.g.,  the  non-striped  muscle  cells  of  the  mesentery  of 
the  newt — that  each  muscle  cell  consists  of  a  delicate 


64  Elements  of  Histology.      [Chap.  vin. 

elastic  sheath,  inside  of  which  is  a  bundle  of  minute 
fibrils,  which  cause  the  longitudinal  striation  of  the  cell. 
These  fibrils  are  the  contractile  portion ;  and  they  are 
contractile  towards  the  nucleus,  with  whose  intranu- 
clear reticulum  they  are  intimately  connected.  When 
the  cell  is  contracted  its  sheath  becomes  transversely 
corrugated  (Fig.  38b). 

79.  The  non-striped  muscular  cells  are  aggregated 
into  smaller  or  larger  bundles  by  an  interstitial  albu- 


Fig.  38b.— A  Non-striped  Muscular  Cell  of  Mesentery  of  Newt. 

Showing  several  places  where  the  muscular  substance  appears  contracted, 
thickened.  At  these  places  the  corrugations  of  the  sheath  are  marked. 
(Atlas.) 

minous  homogeneous  cement  substance,  the  cells  being 
imbricated  with  their  extremities.  The  bundles  may 
form  a  plexus,  or  they  may  be  aggregated  by  fibrous 
connective  tissue  into  larger  or  smaller  groups,  and 
these  again  into  continuous  masses  or  membranes.  In 
the  muscular  coat  of  the  bladder,  in  the  choroidal 
portion  of  the  ciliary  muscle,  in  the  arrector  pili,  in  the 
muscular  tissue  of  the  scrotum,  very  well  marked 
plexuses  of  bundles  of  non-striped  muscular  cells  may 
be  met  with.  In  the  muscularis  mucosae  of  the 
stomach  and  intestines,  in  the  outer  muscular  coat  of 
the  same  organs,  in  the  uterus,  bladder,  &c,  occur 
continuous  membranes  of  non-striped  muscular  tissue. 

When  the  muscular  cells  form  larger  bundles  they 
are  more  or  less  pressed  against  one  another,  and, 
therefore,  in  a  cross  section  appear  of  a  polygonal 
outline. 

80.  Non-striped  muscular  tissue  is  found  in  the 
following  places  :  in  the  muscularis  mucosae  of  the 
oesophagus,  stomach,  small  and  large  intestine ;  in  the 


chap,  viii.]    Non-striped  Muscular  Tissue. 


65 


^s 


r"~-^ 


outer  muscular  coat  of  the  lower  two-thirds  or  half 
of  the  human  oesophagus ;  in  that  of  the  stomach,  small 
and  large  intestine;  in  the  tissue  of  the  pelvis  and 
outer  capsule  of  the  kidney ;  in  the  muscular  coat  of 
the  ureter,  bladder,  and  urethra;  in  the  tubules  of 
the  epididymis,  in  the  vas  de- 
ferens, vesiculse  seminalis  and 
prostate  ;  in  the  corpora  caver- 
nosa, and  spongiosa;  in  the 
tissue  of  the  ovary,  and  in  the 
ligamentum  latum ;  in  the  mus- 
cular coat  of  the  oviduct,  the 
uterus  and  vagina ;  in  the  soft 
or  posterior  part  of  the  wall  of 
the  trachea ;  in  the  large  and 
small  bronchi,  in  the  alveolar 
ducts  and  infundibula  of  the 
lung ;  in  the  pleura  pulmonalis 
(guinea-pig) ;  in  the  peritoneum 
of  the  frog  and  newt,  in  the 
upper  part  of  the  upper  eye-lid, 

and  in  the  fissura  orbitalis ;  in  the  sphincter  and 
dilatator  pupillse,  and  the  ciliary  muscle ;  in  the 
capsule  and  tra,beculse  of  the  spleen,  and  the  trabecule 
of  some  of  the  lymphatic  glands ;  in  the  arrector  pili, 
and  sweat  glands  of  the  skin,  the  tunica  dartos  of 
the  scrotum ;  in  the  tissue  of  the  nipple  of  the  breast ; 
in  the  large  ducts  of  the  salivary  and  pancreatic 
gland  ;  and  in  the  muscular  coat  of  the  gall  bladder, 
the  hepatic  and  cystic  duct.  The  aorta  and  the 
arteries  have  a  larger  amount  of  non-striped  muscular 
tissue,  the  veins  and  lymphatics  a  smaller. 

81.  As  regards  length,  the  muscular  cells  vary 
within  considerable  limits  (from  y1^  to  -^^  of  an  inch), 
those  of  the  intestine,  stomach,  respiratory,  urinary,  and 
genital  organs  being  very  long,  as  compared  with 
those  of  the  blood-vessels,  which  are  sometimes  only 

F 


Fig.  33.— Prom  a  Transverse 
Section  through  Bundles 
of  Non-striped  Muscular 
Tissue  of  the  Intestine. 

The  muscular  cells  being  spindle- 
shaped  are  cut  at  various 
heights  ;  the  large  corpuscles 
of  the  figure  correspond  to  the 
middle,  the  small  ones  to  the 
extremities,  of  the  muscle- 
cells.    (Atlas.) 


66  Elements  of  Histology.         [Chap.  ix. 

twice  or  thrice  as  long  as  they  are  broad,  and  at  the 
same  time  branched  at  their  extremities. 

Non-striped  muscular  tissue  is  richly  supplied  with 
blood-vessels,  the  capillaries  forming  oblong  meshes, 
though  their  number  is  not  so  great  as  in  striped 
muscle.  The  nerves  of  non-striped  muscle  are  all 
derived  from  the  sympathetic  ;  their  distribution  and 
termination  will  be  described  in  a  future  chapter. 


CHAPTER   IX. 

STRIPED   MUSCULAR   TISSUE. 

82.  This  tissue  is  composed  of  extremely  long  (up 
to  l|-2  inches)  more  or  less  cylindrical  fibres,  of  a 
diameter  varying  between  ~o  to  g^-  of  an  inch  ;  they 
appear  transversely  striated.  These  are  the  striped 
muscular  fibres.  They  are  held  together  by  delicate 
bundles  of  fibrous  connective  tissue,  with  the  ordinary 
connective  tissue  cells — endomysium — so  as  to  form 
larger  or  smaller  bundles  ;  these  again  are  aggregated 
together  by  stronger  bands  and  septa  of  fibrous  con- 
nective tissue — perimysium — into  groups,  and  these 
into  the  fascicles  or  divisions  of  an  anatomical  muscle. 
The  fibrous  connective  tissue,  including  the  perimysium 
tissue,  is  the  carrier  of  the  larger  vascular  and  nervous 
branches.  The  endomysium  contains  the  capillaries, 
which  form  very  rich  networks  with  elongated  meshes, 
and  are  always  situated  between  the  individual 
muscle  fibres.  The  capillaries  and  veins  appear  very 
wavy  and  twisted  in  the  contracted  bundles,  and 
straighter  in  the  uncontracted  bundles.  The  small 
vessels  are  provided  here  and  there  with  peculiar  saccu- 
lar dilatations,  winch  act  as  a  sort  of  safety  receptacles 


chap,  ix.]      Striped  Muscular    Tissue. 


67 


for  the  blood  when,  during  a  sudden  maximal  contrac- 
tion, it  is  pressed  out  from  some  of  the  capillaries. 

83.  Each  muscular  fibre  during  contraction  be- 
comes shorter  and  thicker.  In  the  living  uninjured 
muscular  fibres,  spontaneously  or  after  the  application 
of  a  stimulus,  a  contraction  starts  at  one  point  and 
passes  over  the  whole  muscular  fibre  like  a  wave — 
contraction  wave — the  progress  of  which  is  noticeable 
by  the  thickening,  gradually  and  rapidly,  shifting  along 
the  fibre,  the  part  behind  resuming  its  previous  diameter. 

84.  When  looked  at  in  the  fresh  state,  or  after  the 
action  of  certain  re-agents,  the  muscular  fibre  shows  the 
folio  wing  parts 


L 


nmummmmmnmir 

!l!ii!!i||l  N  n  1 1 1 1 1 1 1 1  H  Mi! 
iiiiiUiiisisiiiiiiiiiisiiiil  , 


(Fig.  40)  :  (1)  a 
transparent  ho- 
mogeneous deli- 
cate  elastic 
sheath,  the  sar- 
colemma ;  (2) 
dark  delicate 
lines  stretching 
across  the  fibre 
at  regular  inter- 
vals, so  as  to 
sub-divide  the 
space  within 
the  sarcolemma 
into  uniform 
transverse  com- 
partments, the 
muscular  com- 
partments of 
Krause.  These 
dark  lines  are 
the  membranes 
of  Krause.  Un- 
der a  high  power  they  seem  permeated  or  broken  up  by 


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B 


Fig.  40.— Striped  Muscular  Fibres  of  the  Water- 
Beetle  (Hydrophilus). 

a,  Sarcolemma ;  6,  Krause's  membrane.  The  sarcous 
elements  are  well  seen.  In  a  the  oblong  nuclei  of 
the  muscle-corpuscles  are  shown.  In  b  the  sarco- 
lemma has  become  unnaturally  raised  from  the  mus- 
cular contents.  The  contractile  discs  are  well  shown ; 
so  also  are  the  sarcous  elements.    (Atlas.) 


68  Elements  of  Histology.         [Chap.  ix. 

a  great  number  of  fine,  clear,  longitudinal  lines  (see  be- 
low), and  therefore  under  these  conditions  seem  to  be 
made  up  of  one  row  of  granules.  The  membranes  of 
Krause  appear  fixed  to  the  sarcolemma,  so  that  while 
a  fibre  contracts,  or  while  it  is  contracted  or  shrunk, 
owing  to  the  action  of  hardening  re-agents,  or  merely 
in  consequence  of  being  detached  from  its  fixations,  its 
surface  is  not  smooth,  but  regularly  and  transversely 
undulating,  the  valleys  being  caused  by  the  attachment 
of  the  membranes  of  Krause  to  the  sarcolemma. 
On  stretching  a  fibre  beyond  its  natural  passive  state, 
the  surface  becomes  also  uneven  and  undulating,  but 
in  a  reverse  manner  from  the  above. 

85.  These  two  membranous  structures  represent, 
as  it  were,  the  framework.  In  the  muscular  com- 
partments is  contained  the  muscular  substance,  which 
again  consists  of  (a)  the  contractile  or  chief  substance 
(Rollett),  which  is  a  dim,  broad,  highly  refractive, 
doubly  refractive  disc,  occupying  the  greater  part  of  a 
compartment,  except  a  thinner  or  thicker  layer  at  the 
side  of  Krause's  membrane.  This  layer  is  (6)  a  trans- 
parent homogeneous  fluid  substance,  forming  the  lateral 
disc  of  Engelmann,  or  the  secondary  substance  of 
Rollett.  It  is  isotropous.  In  this  lateral  disc  occa- 
sionally a  transverse  row  of  granules  appears  present, 
but  this  is  by  no  means  of  constant  occurrence.  The 
contractile  disc  seems  homogeneous,  but  is  in  reality 
composed  of  prismatic  or  rod-shaped  elements,  the  sar- 
cous  elements  of  Bowman,  each  being  as  long  as  the  con- 
tractile disc.  They  are  very  close,  and  there  is  left 
between  them  in  the  fresh  and  living  state  an  exceed- 
ingly minute  layer  of  a  homogeneous  transparent 
interstitial  substance,  identical  with  that  of  the  lateral 
disc.  After  death  and  shrinking  of  the  sarcous 
elements,  this  interstitial  substance  is  more  marked, 
and  is  then  easily  perceived  as  longitudinal  clear 
lines   separating   the   sarcous   elements   in   the   indi- 


Chap,  ix.]      Striped  Muscular  Tissue.  69 

vidual  compartments.  The  total  appearance  pro- 
duced is  that  of  longitudinal  striation,  the  sarcous  ele- 
ments of  successive  compartments  forming  fibrils — 
called  the  primitive  fibrils.  Sometimes  in  hardened 
muscular  fibres  the  substance  of  the  sarcous  elements 
shows  a  middle  transparent  portion  for  the  whole 
contractile  disc ;  this  appears  to  form  a  distinct 
median  transparency,  known  as  the  median  disc  of 
Hensen. 

86.  Of  course,  each  such  fibril  is  a  successive  row 
of  sarcous  elements,  with  the  corresponding  portion  of 
Krause's  membranes,  and  the  adjacent  portions  of  the 
lateral  discs.  Generally,  each  fibril  is  thinnest  at  the 
point  of  Krause's  membrane  and  lateral  discs,  and 
thicker  at  the  part  corresponding  to  the  sarcous  ele- 
ments, so  that  in  reality  it  is  of  a  moniliform  shape 
(Haycraft).  This  varicose  condition  is  the  more  appa- 
rent the  shorter  and  thicker  the  individual  sarcous 
elements  are  (Fig.  43a,  b  and  c). 

These  differentiations  due  to  structure  alone  are 
sufficient  to  produce  a  transverse  striation  of  the  mus- 
cular fibres;  but  it  must  be  borne  in  mind  that  a  fibre 
when  contracted  or  shrunk,  even  in  the  smallest  degree, 
would  show  a  transverse  striation  due  to  the  above- 
mentioned  undulating  surface.  Any  other  fibre  with  a 
moniliform  shape  would  show  the  same  transverse 
striation  (Haycraft)  ;  and  that  usually  observed  on 
hardened — i.e.,  shrunk  and  more  or  less  contracted — 
fibres,  may  be  accounted  for  in  this  way.  Fibres 
stretched  or  prevented  from  shrinking  generally  show 
pronounced  longitudinal  striation,  but  also  very  faint 
cross  strise ;  these  latter  are  due  to  the  structural 
differences. 

87.  On  observing  a  transverse  section  through  a 
fresh  and  living  muscular  fibre,  the  muscular  substance 
inside  the  sarcolemma  appears  as  a  transparent  ground- 
glass-like  substance,  crossed  here  and  there  by  bright 


7° 


Elements  of  Histology. 


[Chap.  IX. 


lines.  These  lines  gradually  increase  in  number,  and 
to  join  that  ultimately  they  form  a  dense  network. 
Thus  a  more  or  less  regular  pattern  of  small  polygonal 
fields  is  produced,  which  are  styled  Cohnheim's  areas  or 

fields  (Fig.  41).  Each  corre- 
sponds to  the  end-view  or 
optical  section  of  a  sarcous 
element  prism,  and  is  granu- 
lar, as  if  composed  of  a 
bundle    of     minute    fibrils. 


Fig.    41.  —  Striped     Muscular 
Fibres  in  Cross  Section. 

Each  fibre  is  limited  by  the  sarco- 
lemma;  the  muscular  substance 
is  differentiated  into  Cohnheim's 
areas.    (Atlas.) 


If  this  be  the  case,  each 
sarcous  element  will  have  to 
be  considered  as  a  bundle 
of  rods.  The  bright  lines 
producing  the  Cohnheim's 
fields  are  the  interstitial 
substance.  When  a  muscle 
fibre  shrinks,  after  death 
or  after  some  hardening  re- 
agents, Cohnheim's  fields 
shrink  into  small  circular  areas,  separated  by  a  rela- 
tively large  amount  of  the  interstitial  substance. 

88.  During  contraction  the  cross  striation  is  much 
narrower,  the  dim  disc  becoming  shorter  in  the  long 
diameter  of  the  fibre,  but  broader  in  the  transverse 
direction. 

The  broader  the  lateral  disc  in  a  fibre,  the  more 
apart  from  one  another  are  the  dim  or  contractile 
discs. 

On  the  surface  of  the  substance  of  the  muscle 
fibres,  but  within  the  sarcolemma,  are  seen  isolated 
oblong  nuclei,  which  belong  to  small  protoplasmic, 
more  or  less  branched  corpuscles — the  muscle  cor- 
puscles. In  the  adult  fibres  these  are  few  and  far 
between ;  in  the  young  and  growing  fibres  they  are 
numerous  and  large.  Their  protoplasm  is  the  sub- 
stance which,  becoming  converted  into  the  muscular 


chap,  ix.]       Striped  Muscular  Tissue.  7 1 

substance,  is  the  material  at  the  expense  of  which 
new  fibres  are  formed,  or  fibres  already  formed 
become  thickened,  as  is  the  case  when  muscle  fibres 
are  kept  at  constant  work. 

In  the  muscular  fibres  of  man  and  most  verte- 
brates (except  the  fibres  of  the  heart),  the  muscular 
corpuscles  are  situated  on  the  surface  of  the  muscular 
substance  ;  but  in  invertebrates  (especially  insects  and 
Crustacea)  they  are  often  found,  in  the  central  part 
of  the  fibres,  and  here  they  are  occasionally  seen 
forming  almost  a  continuous  cylindrical  mass  of  nu- 
cleated protoplasmic  cells. 

89.  In  the  embryo  the  muscular  fibres  are  de- 
veloped from  spindle-shaped,  nucleated  cells  (Remak, 
Weissmann,  Kolliker).  One  spindle-shaped  cell  with 
an  oval  nucleus  grows  rapidly  in  length  and  thick- 
ness, its  nucleus  divides  repeatedly,  and  the  offspring 


Fig.  42. — A  Striped  Muscular  Fibre  of  the  Diaphragm  of  a 
Guinea-pig. 

The  muscle-corpuscles  are  much  increased  in  size   and  numbers;    they  are 
probably  used  here  for  the  new  formation  of  muscular  substance.    (Atlas.) 


become  shifted  from  one  another  as  the  cell  con- 
tinues to  grow  in  length.  The  protoplasmic  sub- 
stance all  along  one  side  of  the  cell  gives  origin  to 
the  muscular  substance — sarcous  elements  and  lateral 
disc — while  a  small  rest  of  protoplasm  remains  col- 
lected around  the  nucleus  as  the  muscle  corpuscle. 
This   protoplasm    continues   to   increase   in    amount, 


72 


Elements  of  Histology. 


[Chap.  IX. 


muscle  fibres, 
direction  into 
become    richly 

terminate     in 


and  then  the  increment  again  changes  into  muscular 
substance  (Fig.  42).  In  this  way  the  muscular  fibre 
increases  in  thickness.  Thus  one  spindle-shaped 
embryo  cell  gives  rise  to  one  muscular  fibre,  which, 
at  first  very  slender,  continues  to  grow  in  thickness 
by  the  active  growth  of  the  muscle  corpuscles.     The 

sarcolemma   appears  to  be   formed   from 

cells  other  than  muscle  cells. 

90.  The  striped  muscular  fibres,  taken 
as  a  whole,  are,  as  a  rule,  spindle-shaped, 
becoming  gradually  thinner  towards  their 
ends.  They  are  branched  in  some  excep- 
tional cases — e.g.,  in  the  tongue ;  here 
the  extremities  of  the 
passing  in  a  transverse 
the  mucous  membrane, 
branched. 

91.  Muscular  fibres 
tendons,  either  by  the  whole  fibre  passing 
into  a  bundle  of  connective  tissue  fibrils 
(Fig.  43),  or  by  the  fibre  ending  abruptly 
with  a  blunt,  conical  end,  and  becoming 
here  fixed  to  a  bundle  of  connective  tissue 
fibrils.  The  individual  fibres  have  only, 
as  mentioned  above,  a  relatively  limited 
length,  so  that,  following  an  anatomical 
fascicle  from  one  point  of  its  insertion  to 
the  other,  we  find  some  muscle  fibres 
terminating,  others  originating.  This 
takes  place  in  the  following  way  :  the 
contents  of  a  fibre  suddenly  terminate, 
while  the  sarcolemma,   as  a  fine  thread, 

becomes  interwoven  with  the  fine  connective  tissue 
between  the  muscular  fibres. 

92.  The  striped  muscular  fibres  of  the  heart 
(auricles  and  ventricles)  and  of  the.  cardiac  ends  of 
the  large  veins  (the  pulmonary  veins  included)  differ 


Fig.  43.  —  Two 
Striped  Mus- 
cular Fibres 
passing  into 
Bundles  of 
Fibrous  Tis- 
sue. 

Termination  in 
Tendon.  (Hand- 
book.) 


Chap,  ix.]       Striped  Muscular  Tissue. 


73 


from  other  striped  muscular  fibres  in  the  following 
respects: — (1)  They  possess  no  distinct  sarcolemma. 

(2)  Their  muscle  corpuscles  are  in  the  centre  of  the 
fibres,   and  more  numerous  than  in  ordinary  fibres. 

(3)  They  are  very  richly  branched,  each  fibre  giving  off 
all  along  its  course  short  branches,  or  continually  divid- 
ing   into    smaller 

fibres    and    form-      ^  |p^  \0\  I1  :  KB 
ing    a    close    net- 
work (Fig.  43a.)  A 
transverse  section 


through  a  bundle 
of  such  fibres 
shows,  therefore, 
their  cross  sections 
irregular  in  shape 
and  size.  (4)  Each 
nucleus  of  a  muscle 
corpuscle  occupies 
the  centre  of  one 
prismatic  portion ; 
each  fibre  and  its 
branches  thus 
appear  composed 
of  a  single  row  of 
such  prismatic 
portions,  and  they 
seem  separated 
from  one  another 
— at  any  rate  in  an 
early  stage — by  a  septum  of  a  transparent  substance. 

93.  Muscular  fibres  seem  either  markedly  pale 
or  markedly  red  (Ranvier) ;  in  the  former  {e.g., 
quadratus  lumborum,  or  adductor  magnus  femoris 
of  rabbit)  the  transverse  striation  is  more  distinct 
and  the  muscular  corpuscles  less  numerous,  than 
in     the     latter     {e.g.,    semi-tendinosus     of     rabbit, 


B 


Striped  Muscular  Fibres  of  the 
Heart  of  Mouse. 

A,  Showing  the  branching  of  the  fibres  and  their 
anastomosis  in  networks ;  b,  part  of  a  thin  fibre, 
highly  magnified,  showing  the  moniliform 
primitive  fibrillar:  c,  one  primitive  fibrilla 
more  highly  magnified. 


Fig.  43a. 


74  Elements  of  Histology.  [Chap.  x. 

diaphragm).  Here  the  longitudinal  striation  ap- 
pears very  distinct,  but  these  differences  are  not 
constant  in  other  muscular  fibres  of  other  animals 
(E.  Meyer). 

94.  Briicke  has  shown  that  striped  muscular  fibres 
are  doubly  refractive,  like  uniaxial  positive  crystals 
(rock  crystal),  the  optical  axis  coinciding  with  the 
long  axis  of  the  fibres.  The  lateral  disc  and  inter- 
stitial substance  are  isotropous,  the  sarcous  elements 
(Briicke)  and  Krause's  membrane  (Engelmann)  being 
doubly  refractive.  The  sarcous  elements  are,  how- 
ever, not  the  ultimate  optical  elements,  but  must  be 
considered  as  composed  of  disdiaclasts,  the  real  doubly 
refractive  elements  (Briicke). 


CHAPTER  X. 

THE    HEART    AND    BLOOD-VESSELS. 

95.  (a)  The  heart  consists  of  an  outer  serous 
covering  (the  visceral  pericardium),  an  inner  lining 
(the  endocardium),  and  between  the  two  the  muscular 
wall  (Fig.  44).  Underneath  the  pericardium  and  en- 
docardium is  a  loose  connective  tissue,  called  the  sub- 
pericardial  and  subendocardial  tissue  respectively. 

The  free  surface  of  both  the  pericardium  and 
endocardium  has  an  endothelial  covering,  like  other 
serous  membranes — i.e.,  a  single  layer  of  transparent 
nucleated  cell  plates  of  a  more  or  less  polygonal  or 
irregular  shape.  The  ground- work  of  these  two  mem- 
branes is  fibrous  connective  tissue,  forming  a  dense 
texture,  and  in  addition  there  are  many  elastic  fibres 
composing  networks.  Capillary  blood-vessels,  lymphatic 


chap,  x.]     The  Heart  and  Blood-vessels. 


75 


vessels,  and  small  branches  of  nerve-fibres  are  met 
with  everywhere.  The  subpericardial  and  subendo- 
cardial tissues  consist  of  loosely  connected  trabecule  of 
fibrous  connective  tissue,  forming  a  continuity  with 
the  intermuscular  connective  tissue  of  the  muscular 
part    of    the    heart. 

a, 

6^ 


The  former  contains 
in  many  places 
groups  of  fat  cells. 

96.  On  the  free 
surface  of  the  papil- 
lary muscles,  in  some 
parts  of  the  surface 
of  the  trabecule  ear- 
ner, and  at  the  inser- 
tion of  the  valves, 
the  endocardium  is 
thickened  by  ten- 
dinous connective 
tissue.  The  valves 
themselves  are  folds 
of  the  endocardium, 
and  contain  in  their 

essential  parts  fibrOUS    Fig.  44.— Transverse  Section  through  the 

Auricle  of  the  Heart  of  a  Child. 


connective  tissue,  to 


a,  Endothelium  lining  the  endocardium ;  5,  en- 
docardium ;  c,  muscular  bundles  cut  trans- 
versely ;  d,  muscular  bundles  cut  longitu- 
dinally ;    e,  pericardial  covering. 


which,    especially  in 

the  semilunar  valves, 

numerous         elastic 

fibres  are  added.     The  muscular  tissue  of  the  wall 

of  the  auricle  penetrates  a  short  way  into  the  auriculo- 

ventricular  valves. 

All  the  cordse  tendinese  and  the  valves  are  of  course 
covered  on  their  free  surfaces  with  endothelium. 

Special  tracts  of  muscle  fibres   occur  in  the  sub- 
endocardial tissue. 

The  fibres  of  Purkinje  are  peculiar  fibres  occurring 
in    the  subendocardial  tissue  in  some  mammals  and 


76  Elements  of  Histology.  [Chap.  x. 

birds  (not  in  man).  They  are  thin,  transversely  striped, 
muscular  fibres,  the  central  part  of  which  is  a  con- 
tinuous mass  of  protoplasm,  with  nuclei  at  regular 
intervals,  the  same  as  is  the  case  with  some  skeletal 
muscular  fibres  of  insects. 

97.  The  muscular  fibres  forming  the  proper  wall 
of  the  heart,  the  structure  of  which  has  been  described 
in  the  previous  chapter,  are  grouped  in  bundles 
separated  by  vascular  fibrous  connective  tissue.  In  the 
ventricles  the  bundles  are  aggregated  into  more  or  less 
distinct  lamellse. 

Like  other  striped  muscular  fibres,  those  of  the 
wall  of  the  heart  are  richly  supplied  with  blood-vessels 
and  lymphatics.  The  endocardium  and  valves  and  the 
pericardium  possess  their  own  systems  of  capillaries. 

The  lymphatics  form  a  pericardial  and  an  endo- 
cardial network,  the  muscular  substance  of  the -heart 
having  numerous  lymphatics  in  the  shape  of  lymph 
clefts  between  the  muscular  bundles,  and  also  typical 
networks  of  tubular  lymphatics. 

98.  The  nerve  branches  of  the  plexus  cardiacus 
form  rich  plexuses.  In  connection  with  some  of 
them  are  found  numerous  collections  of  ganglion  cells 
or  ganglia.  These  are  very  numerous  in  the  nerve 
plexus  of  the  auricular  septum  of  the  frog's  heart  (Lud- 
wig,  Bidder),  and  in  the  auriculo-ventricular  septum 
of  the  frog  (Dogiel).  In  man  and  mammals  numerous 
ganglia  are  found  on  the  subpericardial  nerve  branches, 
chiefly  at  the  point  of  junction  of  the  large  veins  with 
the  heart,  and  at  the  boundary  between  the  auricles 
and  the  ventricles. 

99.  (b)  The  arteries  (Fig.  45)  consist  of :  (a)  an 
endothelial  layer  lining  the  lumen  of  the  vessel ;  (6)  an 
intima  consisting  of  elastic  tissue;  (c)  a  media,  con- 
taining a  large  proportion  of  non-striped  muscular  cells 
arranged  chiefly  in  a  transverse,  i.e.,  circular,  manner; 
and    (d)    an   adventitia   composed   chiefly  of  fibrous 


chap,  x.]     The  Heart  and  Blood-vessels. 


77 


connective  tissue,  with  an  admixture  of  networks  of 
elastic  fibres. 

(a)  The  endothelium  is  a  continuous  single  layer 
of  flattened  elon-  e 
gated  cell  plates,  i 

(b)  The  inti 
ma  in  the  aorta 
and  large  arteries 
is  a  very  com- 
plex structure,  m. 
consisting  of  an 
innermost  layer 
of  fibrous  con- 
nective      tissue, 

is  the 
longitu- 
jibrous 


which 
11  inner 
dinal 


Isi 


e,  Endothelial  lining ;  l,  elastic  intima ;  m,  muscular 
media ;  a,  adventitia  with  numerous  elastic  fibrils, 
cut  in  transverse  section.    (Atlas.) 


layer"  of  Remak, 
outside  of  which 
is  a  more  or  less 

1 0  ng  i  tud  i  n  a  1 1  y-  pig_  45.— From  a  Transverse  Section  through 
arranged     elastic         the  Inferior  Mesenteric  Artery  of  the  Pig. 

membrane.  This 
is  laminated,  and 
composed       of 

fenestrated  elastic  membranes  of  Henle  (see  a  former 
chapter).  The  greater  the  artery  the  thicker  the 
intima.  In  microscopic  arteries  the  intima  is  a  thin 
fenestrated  membrane,  the  fibres  having  distinctly  a 
longitudinal  arrangement. 

(c)  The  media  is  the  chief  layer  of  the  wall  of  the 
arteries  (Fig.  46).  It  consists  of  transversely  arranged 
elastic  lamellae  (fenestrated  membranes  and  networks 
of  elastic  fibres),  and  between  them  smaller  or  larger 
bundles  of  circularly  arranged  muscular  cells.  The 
larger  the  artery  the  more  is  the  relation  of  elastic 
and  muscular  tissue  of  the  media  in  favour  of   the 


78 


Elements  of  Histology. 


[Chap.  x. 


former,  in  the  smaller  arteries  the  reverse  is  the  case. 
In  microscopic  branches  of  arteries  the  media  consists 

almost    entirely   of    cir- 


cular non-striped  muscle 
cells  with  only  few  elas- 
tic fibres. 

100.  In  the  last 
branches  of  the  micro- 
scopic arteries,  the  mus- 
cular media  becomes  dis- 
continuous, inasmuch  as 
the  (circular)  muscular 
cells  are  arranged  not  as 
a  continuous  membrane, 
but  as  groups  of  small 
cells  (in  a  single  layer) 
in  a  more  or  less  alter- 
nate fashion. 

When  the  media 
contracts,  the  intima 
is  placed  in  longitudinal 
folds. 

The  aorta  has,  in  the 
innermost  and  in  the 
outermost  parts  of  the 
media,  numbers  of  lon- 
gitudinal and  oblique 
muscle  cells.  Accord- 
to  Bardeleben,  all 
and     middle-sized 


Fig.  46. — Transverse  Section  through 
a  Microscopic  Artery  and  Vein  in 
the  Epiglottis  of  a  Child. 

A,  The  artery,  showing  the  nucleated 
endothelium,  the  circular  muscular 
media,  and  at « the  fibrous-tissue  adven- 
titia;  v,  the  vein,  showing  the  same 
layers  ;  the  media  is  very  much  thinner 
than  in  the  artery.    (Atlas.) 


ing 
large 


arteries  have  an  inner  longitudinal  muscular  coat. 

101.  Between  the  media  and  the  next  outer  layer 
there  is,  in  larger  and  middle-sized  arteries,  a  special 
elastic  membrane,  the  elastica  externa  of  Henle. 
(d)  The  adventitia  is  a  relatively  thin  fibrous  con- 
nective tissue  membrane.  In  large  and  middle-sized 
arteries  there  are  numbers  of  elastic  fibres  present, 


Chap,  x.]     The  Heart  and  Blood-vessels. 


79 


especially  in  the  part  next  to  the  media ;  they  form 
networks,  and  have  pre-eminently  a  longitudinal 
direction. 

The  larger  the  artery  the  more  insignificant  is  the 
adventitia  as  compared  with  the  thickness  of  media. 

In  microscopic  arteries  (Fig.  47),  the 
adventitia  is  represented  by  thin  bundles 
of  fibrous  connective  tissue  and  branched 
connective  tissue  cells. 

Large  and  middle-sized  arteries  pos- 
sess their  own  system  of  blood-vessels 
(vasa  vasorum),  situated  chiefly  in 
the  adventitia  and  media ;  lymphatic 
vessels  and  lymphatic  clefts  are  also 
present  in  these  coats. 

102.  (c)  The  veins  differ  from  the 
arteries  in  the  greater  thinness  of  their 
wall.  The  intima  and  media  are  similar 
to  those  of  arteries,  only  thinner,  both 
absolutely  and  relatively.  The  media 
contains   in   most    veins    circularly    ar-  Fi&- .  *i-  —  Minute 

J  Microscopic 

ranged  muscular  fibres  ;  they  form  a  con- 


Artery 

,  -  i    e,   Endothelium ;    i, 

tmuous    1  ayer,    as    m  the   arteries,    and    intima ;  m,  nmscu- 

.  t  .        ■.       ,  ,i  -.-I  lar     media,     com 

there  is   between  them   generalfy  more 
fibrous    connective    tissue   than   elastic. 


posed  of  a  single 
layer  of  circular- 
ly-arranged non- 
striped  muscular 
cells ;  a,  adventitia. 
(Atlas.) 


The  adventitia  is  usually  the  thickest  coat, 
and  it  consists  chiefly  of  fibrous  connec- 
tive tissue  (Fig.  46).  The  smallest  veins — i.e.,  before 
passing  into  the  capillaries — are  composed  of  a  lining 
endothelium,  and  outside  this  are  delicate  bundles  of 
connective  tissue  forming  an  adventitia.  The  valves 
of  the  veins  are  folds,  consisting  of  the  endothelium 
lining  the  surface,  of  the  whole  intima,  and  of  part 
of  the  muscular  media. 

103.  There  are  many  veins  that  have  no  muscular 
fibres  at  all,  e.g.,  vena  jugularis — interna  and  externa 
— the  vena   subclavia,    the  veins  of   the  bones   and 


80  Elements  of  Histology.  [Chap.  x. 

retina,  and  of  the  membranes  of  the  brain  and  cord. 
Those  of  the  gravid  uterus  have  only  longitudinal 
muscular  fibres.  The  vena  cava,  azygos,  hepatica, 
spermatica  interna,  renalis  and  axillaris,  possess  an 
inner  circular  and  an  outer  longitudinal  coat.  The  vena 
iliaca,  cruralis,  poplitea,  mesenterica,  and  umbilicalis 
possess  an  inner  and  outer  longitudinal  and  a  middle 
circular  muscular  coat.  The  intima  of  the  venae 
pulmonales  in  man  is  connective  tissue  containing 
circular  bundles  of  non-striped  muscular  cells  (Stieda). 

104.  The  trunk  of  the  venae  pulmonales  possesses 
striped  muscular  fibres,  these  being  continuations  of 
the  muscular  tissue  of  the  left  auricle. 

105.  Hoyer  showed  that  a  direct  communication 
exists  between  arteries  and  veins  without  the  inter- 
vention of  capillaries — as  in  the  matrix  of  the  nail, 
in  the  tip  of  the  nose  and  tail  of  some  mammals,  in 
the  tip  of  the  fingers  and  toes  of  man,  in  the  margin 
of  the  ear  lobe  of  dog  and  cat  and  rabbit. 

In  the  cavernous  tissue  of  the  genital  organs 
veins  make  large  irregular  sinuses,  the  wall  of  which 
is  formed  by  fibrous  and  non -striped  muscular  tissue. 

106.  (d)  The  capillary  blood-vessels  are 
minute  tubes  of  about  ^Vo  ^°  ~3oVo  °^  an  incn  in 
diameter.  Their  wall  is  a  single  layer  of  transparent 
elongated  endothelial  plates,  separated  by  thin  lines  of 
cement  substance  (Fig.  48) ;  each  cell  has  an  oval 
nucleus.  In  fact,  the  wall  of  the  capillaries  is  merely 
a  continuation  of  the  endothelial  membrane  lining 
the  arteries  and  veins. 

In  some  places  the  capillaries  possess  a  special 
adventitia  made  up  of  branched  nucleated  connective 
tissue  cells  (hyaloidea  of  frog,  choroidea  of  mammals), 
or  of  an  endothelial  membrane  (pia  mater  of  brain 
and  cord,  retina  and  serous  membranes),  or  of  adenoid 
reticulum  (lymphatic  glands,  His). 

The  smallest  capillaries  are  found  in  the  central 


chap.x.]    The  Heart  and  Blood-vessels. 


81 


nervous  system,  the  largest  in  the  marrow  of  bone. 
The  capillaries  form  always  networks,  the  richness  and 


Fig.  48. — From  a  Preparation  of  the  Peritoneum,  stained 
with  Nitrate  of  Silver. 

re,  The  endothelium  on  the  free  surface  of  the  membrane ;  5,  the  capillary  blood- 
vessels in  the  membrane  ;  their  wall  is  a  layer  of  endothelium.    (Handbook.) 


rig.  49.— Young  Fat  Tissue  of  the  Omentum,  its  Blood-vessels  injected 
a,  Artery ;  6,  vein ;  c,  network  of  capillaries.    (Handbook.) 

arrangement    of  which  vary  in  the  different  organs, 
according  to  the  nature  and  arrangement  of  the  ele- 
ments of  the  tissue  (Fig.  49). 
G 


82 


Elements  of  Histology. 


[Chap.  x. 


107.  If  capillaries  are  abnormally  distended,  as 
in  inflammation,  or  otherwise  injured,  the  cement  sub- 
stance between  the  endothelial  plates  is  liable  to  give 
way  in  the  shape  of  minute  holes,  or  stigmata,  which 
may  become  larger  holes,  or  stomata.  The  passage 
of  red  blood  corpuscles  (diapedesis),  and  the  migration 
of  white  corpuscles  in  inflammation  through  the 
unbroken  capillaries  and  small  veins,  occur  through 
these  stigmata  and  stomata. 

108.  Young  and  Growing  Capillaries,  both 
of  normal  and  pathological  tissues,  possess  solid  thread- 


Fig.  50. — From  a  Preparation  of  Omentum  of  Eauoit,  after  staining  with 
Nitrate  of  Silver. 

v,  A  minute  vein  ;  a,  solir)  protoplasmic  prolongations  of  the  wall  of  a  capillary, 
connected  with  connective  tissue  corpuscles ;  c,  a  solid  young  sprout.    (Atlas.) 

like  shorter  or  longer  nucleated  protoplasmic  processes 
(Fig.  50),  into  which  the  canal  of  the  capillary  is 
gradually  prolonged,  so  that  the  thread  becomes  con- 


Chap.x.]    The  Heart  and  Blood-vessels. 


83 


verted  into  a  new  capillary  branch.  Such  growing 
capillaries  are  capable  of  contraction  (Strieker). 

All  blood-vessels,  arteries,  veins,  and  capillaries, 
in  their  early  stages,  both  in  embryonal  and  adult  life, 
are  of  the  nature  of  minute  tubes,  the  wall  of 
which  consists  of  a  simple  endothelial  membrane. 
In  the  case  of  the  vessel  becoming  an  artery  or  vein, 
cells  are  added  to  the  outside  of  the  endothelium, 
thus  forming  the  elastic,  muscular,  and  fibrous  con- 
nective tissue  elements  of  the  wall. 

109.  In  the  first  stage,  both  in  the  embryo  and 
in  the  adult,  the 
vessel  is  repre- 
sented by  a  solid 
nucleated  proto- 
plasmic cell,  elon- 
gated or  spindle- 
shaped  or  branch- 
ed. Such  a  cell 
may  be  an  isolated 
cell  of  the  connec- 
tive tissue  inde- 
pendent of  any 
pre-existing  vessel, 
or  it  may  be  a 
solid  protoplasmic 
outgrowth  of  the 
endothelial  wall  of 
an  existing  capil- 
lary vessel  (Fig.  Fig>  5i._Developinsr  Capillary  Blood-vessels 
51).     In  both  Cases  f rom  the  Tail  of  Tadpole. 

it  V>c>pnTnf»«  Tinl  "»  Capillary  vein  with  clumps  of  pigment  in  the  wall ; 
10  ueuuuics  iiui-  ttj  nucieated  protoplasmic  sprout;  l,  solid  anasto- 
i_     gj      out     bv     a     mosis    between    two    neighbouring    capillaries. 

j  (Alius.) 

process  of  vacuola- 

tion ;  isolated  vacuoles  appear  at  first,  but  they 
gradually  become  confluent,  and  thus  a  young  vessel  is 
formed,  at  first  very  irregular  in  outline,  but  gradually 


84  Elements  of  Histology.         [chap.  xi. 

acquiring  more  and  more  of  a  tubular  form.  In  the 
case  of  an  isolated  cell,  its  protoplasmic  processes 
grow  by  degrees  to  the  nearest  capillary,  to  the  wall 
of  which  they  become  fixed,  and  the  cavity  of  the  cell 
finally  opens  through  such  processes  into  that  of  the 
capillary  vessel. 

The  wall  of  young  capillaries  is  granular-looking 
protoplasm  (the  original  cell  substance),  and  in  it 
are  disposed,  in  more  or  less  regular  fashion,  oblong 
nuclei,  derived  by  multiplication  from  the  nucleus  of 
the  original  cell.  In  a  later  stage,  a  differentiation 
takes  place  in  the  protoplasmic  wall  of  the  capillary 
into  cell-plates  and  cement  substance,  in  such  a  way 
that  each  of  the  above  nuclei  appertains  to  one  cell- 
plate,  which  now  represents  the  final  stage  in  the 
formation  of  the  capillary.  Both  in  the  embryo  and 
in  the  adult  a  few  isolated  nucleated  protoplasmic  cells, 
or  a  few  protoplasmic  solid  processes  of  an  existing 
capillary,  may  by  active  and  continued  growth  give 
origin  to  a  whole  set  of  new  capillaries  (Strieker, 
Affanasieff,  Arnold,  Klein,  Balfour,  Ranvier,  Leboucq). 


CHAPTER  XI. 

THE    LYMPHATIC   VESSELS* 

110.  The  large  lymphatic  trunks,  such  as  the 
thoracic  duct,  and  the  lymphatic  vessels  passing  to  and 
from  the  lymphatic  glands,  are  thin-Walled  vessels, 
similar  in  structure  to  arteries.  Their  lining  endothe- 
lium is  of  the  same  character  as  in  an  artery,  and  so  are 
the  elastic  intima  and  the  media  with  its  circular  mus- 
cular tissue,  only  they  are  very  much  thinner  than  in 
an  artery  of  the  same  calibre.     The  adventitia  is  an 


Chap.  XL] 


The  Lymphatic  Vessels. 


85 


exceedingly  thin  connective  tissue  membrane  with  a 
few  elastic  fibres.  The  valves  are  semi-lunar  folds  of 
the  endothelium  and  intima. 

111.  The  lymphatics  in  the  tissues  and  organs 
form  rich  plexuses.  They  are  tubular  vessels,  the  wall 
of  which  is,  like  that  of  a  capillary  blood-vessel,  a  single 
layer  of  endothelial  plates  (Fig.  52).  The  lymphatic 
may  be,  and  often  is,  many  times  wider  than  a  blood 
capillary.     The  endothelial  plates  are  elongated,  but 


Tig.  52. — Lymphatic  Vessels  of  the  Diaphragm  of  the  Dog,  stained  with. 
Nitrate  of  Silver. 

The  endothelium  forming  the  wall  of  the  lymphatics  is  well  shown ;  v,  valves. 

(Atlas.") 

not  so  long  as  in  a  blood  capillary,  with  more  or  less 
sinuous  outlines,  but  this  depends  on  the  amount  of 
shrinking  of  the  tissue  in  which  the  vessel  is  embedded  ; 
when  there  is  no  shrinking  in  the  tissue  or  in  the  vessel, 
the  outlines  of  the  cells  are  more  or  less  straight. 

The  lymphatics  are  supported  by  the  fibrous  con- 
nective tissue  of  the  surrounding  tissue,  which  does 
not,  however,  form  part  of  their  wall. 


86  Elements  of  Histology.         [Chap.  xi. 

112.  The  outline  of  the  vessel  is  not  straight,  but 
more  or  less  moniliform,  owing  to  the  slight  dilatations 
present  below  and  at  the  semi-lunar  valves  ;  these  are 
folds  of  the  endothelial  wall,  and  they  are  met  with  in 
great  numbers.  The  vessel  appears  slightly  dilated 
immediately  below  the  valve,  that  is,  on  the  side 
farthest  from  the  periphery,  or  rootlet,  whence  the 
current  of  lymph  starts. 

113.  Tracing  the  lymphatic  vessels  in  the  tissues 
and  organs  towards  their  rootlets,  we  come  to  more  or 
less  irregular-shaped  vessels,  the  wall  of  which  also 
consists  of  a  single  layer  of  polygonal  endothelial  plates  ; 
the  outlines  are  very  sinuous.  These  are  the  lym- 
phatic capillaries ;  in  some  places  they  are  mere  clefts 
and  irregular  sinuses,  in  others  they  have  more  the 
character  of  a  tube,  but  in  all  instances  they  have 
a  complete  endothelial  lining,  and  no  valves. 

Sometimes  a  blood-vessel,  generally  arterial,  is 
ensheathed  for  a  shorter  or  longer  distance  in  a 
lymphatic  tube,  which  has  the  character  of  a  lym- 
phatic capillary  ;  these  are  the  perivascular  lymphatics 
of  His,  Strieker,  and  others. 

114.  The  rootlets  of  the  lymphatics  are  situ- 
ated in  the  connective  tissue  of  the  different  organs 
in  the  shape  of  an  intercommunicating  system  of 
crevices,  clefts,  spaces,  or  canals,  existing  between  the 
bundles,  or  groups  of  bundles,  of  the  connective  tissue. 
These  rootlets  are  generally  without  a  complete  endo- 
thelial lining,  but  are  identical  with  the  spaces  in 
which  the  connective  tissue  corpuscles  are  situated ; 
where  these  are  branched  cells  anastomosing  by  their 
processes  into  a  network — such  as  the  cornea,  or  serous 
membranes — we  find  that  the  rootlets  of  the  lymphatics 
are  the  lacunae  and  canaliculi  of  these  cells — the  typical 
lymph-canalicular  system  of  von  Recklinghausen.  (Fig. 
53).  The  endothelial  cells  forming  the  wall  of  the 
lymphatic  capillaries  are  directly  continuous  with  the 


Chap,  xi.]         The  Lymphatic   Vessels. 


87 


connective  cells  situated  in  the  rootlets.  In  tendons 
and  fasciae  the  minute  lymphatics  lie  between  the 
bundles,  and  have  the  shape  of  continuous  long  clefts 


Fig.  53.— From  a  Silver-stained  Preparation  of  the  Central  Tendon  of 
the  Eab bit's  Diaphragm.  Showing  the  direct  connection  of  the 
Lymph- canalicular  System  of  the  Tissue  with  the  Lymphatic 
Capillaries. 

a,  Lymphatic  vessel ;  b,  lymphatic  capillar}'  lined  with  '  sinuous  '  endothelium. 

(Handbook.) 


or  channels  ;  in  striped  muscular  tissue  they  have  the 
same  character,  being  situated  between  the  muscular 
fibres. 

The  passage  of  plasma  from  the  minute  arteries 
and  capillary  blood-vessels  into  the  lymph-rcotlets 
situated  in  the  tissues,  and  thence  into  the  lymphatic 


88 


Elements  of  Histology. 


[Chap.  XI. 


capillaries  and  lymphatic  vessels,  represents  the  natural 
current  of  lymph  irrigating  the  tissues. 

115.  Lymph  cavities.— In  some  places  the  lym- 
phatic vessels  of  a  tissue  or  organ  are  possessed  of,  or 
connected  with,  irregularly-shaped  large  sinuses,  much 
wider  than  the  vessel  itself ;  these  cavities  are  the 
lymph  sinuses,  and  their  wall  is  also  composed  of  a 
single  layer  of  more  or  less  polygonal  endothelial 
plates  with  very  sinuous  outlines.  Such  sinuses  are 
found  in  connection  with  the  subcutaneous  and  sub- 
mucous lymphatics,  in  the  diaphragm,  mesentery,  liver, 
lungs,  &c.  On  the  same  footing — i.e.,  as  lymph 
sinuses — stand  the  comparatively  large  lymph  cavities 
in  the  body,  such  as  the  subdural  and  subarachnoidal 

spaces  of  the  central 
nervous  system,  the 
synovial  cavities,  the 
cavities  of  the  tendon- 
sheaths,  the  cavity  of 
the  tunica  vaginalis 
testis,  the  pleural, 
pericardial,  and  peri- 
toneal cavities.  In 
batrachian  animals, 
e.g.,  frogs,  the  skin  all 
over  the  trunk  and 
extremities  is  sepa- 
rated from  the  sub- 
jacent fasciae  and 
muscles  by  large  bags 
or  sinuses — the  sub- 
cutaneous lymph  sacs. 
These  sinuses  are  shut 
Between  the  trunk 
and  the  extremities,  and  on  the  latter,  the  septa 
generally  occur  in  the  region  of  the  joints.  In 
female  frogs  in  the   mesogastrium  smaller  or  larger 


Fig.  54. — Stomata,  lined  with.  Germi- 
nating Endothelial  Cells,  as  seen 
from  the  Cisternal  Surface  of  the 
SeptumCisternae  Lymphaticse  Magnse 
of  the  Frog.    (Handbook.) 


off  from  one  another  by  septa, 


Chap,  xi.]         The  Lymph  a  tic   Vessels. 


89 


cysts  lined  with  ciliated  endothelium  are  sometimes 
found.  Behind  the  peritoneal  cavity  of  the  frog, 
along  and  on  each  side  of  the  vertebral  column,  exists 
a  similar  large  lymph  sinus,  called  the  cisterna  lympha- 
tica  magna. 

116.  In  all  instances  these  cavities  are  in  direct 
communication  with 
the  lymphatics  of  the 
surrounding  parts  by 
holes  or  open  mouths 
(stomal),  often  lined 
by  a  special  layer  of 
polyhedral  endothe- 
lial cells — germinat- 
ing cells  (Figs.  54, 
55).  Such  stomata 
are  numerous  on  the 
peritoneal  surface  of 
the  central  tendon  of 
the  diaphragm,  in 
which  are  found 
straight  lymph  chan- 
nels     between     the 

tendon  bundles,  and  these  channels  communicate  here 
and  there  with  the  free  surface  by  stomata.  A 
similar  arrangement  exists  on  the  costal  pleura,  the 
omentum,  and  the  cisterna  ]ymphatica  magna  of  the 
frog.     (See  Chapter  IY.) 

117.  The  serous  membranes  consist  of  a 
matrix  of  fibrous  connective  tissue  with  networks  of 
fine  elastic  fibres ;  they  contain  networks  of  blood 
capillaries  and  numerous  lymphatic  vessels  arranged  in 
(superficial  and  deep)  plexuses.  Those  of  the  pleura 
costalis — or  rather,  intercostalis — and  of  the  diaphragm 
and  pleura  pulmonalis,  are  most  numerous.  They  are 
important  in  the  process  of  absorption  from  the  pleural 
and  peritoneal  cavity  respectively.    Lymph  and  lymph 


Fig.  55. — Endothelium  and  Stomata  of 
the  Peritoneal  Surface  of  the  Septum 
Cistern  Lymphatic  Magnse  of  the 
Frog.    (Handbook.) 


90  Elements  of  Histology.         [Chap.  xi. 

corpuscles,  and  other  formed  matter,  are  readily  taken 
tip  by  the  stomata  (see  Fig.  20)  and  brought  into  the 
lymphatics,  and  in  this  the  respiratory  movement  of 
the  intercostal  muscles,  of  the  diaphragm,  and  of 
the  lungs  respectively,  produces  the  result  of  the 
action  of  a  pump. 

118.  There  is  a  definite  relation  between  the 
lymphatics  and  the  epithelium  covering  the  mucous 
membranes  and  lining  the  various  glands  and  between 
the  endothelium  covering  serous  membranes  and  that 
lining  vessels  and  lymph  cavities — viz.,  the  albumin- 
ous semifluid  cement  substance  (see  former  chapters) 
between  the  epithelial  and  endothelial  cells  is  the 
path  by  which  fluid  and  formed  matter  pass  between 
the  surfaces  and  the  lymph-canalicular  system,  the 
latter  being  the  rootlets  of  the  lymphatics. 

119.  Liympli  taken  from  the  lymphatics  of  dif- 
ferent regions  differs  in  composition  and  structure. 
That  from  the  thoracic  duct  contains  a  large 
amount  of  colourless  or  white  corpuscles — lymph  cor- 
puscles— each  of  which  is  a  protoplasmic  nucleated  cell 
similar  in  aspect  and  nature  to  a  white  blood  corpuscle. 
They  are  of  various  sizes,  according  to  the  stage  of 
ripeness.  The  smaller  contain  one,  some  of  the  larger 
contain  two  and  three,  nuclei.  The  latter  show  more 
pronounced  amoeboid  movement  than  the  small  ones. 
A  few  red  corpuscles  are  also  met  with.  Granular 
and  fatty  matter  is  present  in  large  quantities  during 
and  after  digestion. 

In  the  frog  (and  also  in  other  lower  vertebrates, 
e.g.,  reptiles)  there  exist  certain  small  vesicular  lymph 
cavities,  about  an  eighth  of  an  inch  in  diameter, 
which  show  rhythmic  pulsation  ;  they  are  called  lymph 
hearts.  On  each  side  of  the  os  coccygis  and  underneath 
the  skin  is  a  pulsating  posterior  lymph  heart.  The 
anterior  lymph  heart  is  oval,  and  situated  on  each 
side  between  the  processus  trans  vers  us  of  the  third 


Chap,  xi.]         The  Lymphatic  Vessels. 


9i 


and  fourth  vertebra;  it  is  slightly  smaller  than  the 
posterior  one.  The  lymph  hearts  have  an  efferent  ves- 
sel, which  is  a  vein,  and  from  them  the  venous  system 


Fig.  56. — Developing  Lymph-capillaries  in  the  Tail  of  Tadpole. 
a,  Solid  nucleated  protoplasmic  branches  not  yet  hollowed  out.    (Atlas.) 


of  the  neighbourhood  can  be  easily  injected,  whereas 
the  reverse  is  not  possible.  They  are  lined  with  an 
endothelium  like  the  lymph  sacs,  and  in  their 
wall  they  possess  plexuses  of  striped,  branched, 
muscular  fibres.  The  nerve  fibres  terminate  in  these 
striped  muscular  fibres  in  the  same  manner  as  in  those 
of  other  localities.     (Ranvier.) 


92  Elements  of  Histology.        [Chap.  xn. 

120.  Lymphatic  vessels  are  developed  and  newly- 
formed  under  normal  and  pathological  conditions  in 
precisely  the  same  way  as  blood-vessels.  The  accom- 
panying woodcut  (Fig.  56)  shows  this  very  well.  We 
have  also  here  to  do  with  the  hollowing  out  of  (con- 
nective tissue)  cells  and  their  processes  previously 
solid  and  protoplasmic. 


CHAPTER  XII. 

SIMPLE    LYMPHATIC    GLANDS. 

121.  Under  this  name  are  to  be  considered  the 
blood-glands  of  His,  or  the  conglobate  gland  sub- 
stance of  Henle,  or  the  lymph  follicles  (Kolliker, 
Huxley,  Luschka).  The  ground-substance  of  all 
lymphatic  glands,  simple  as  well  as  compound  (see 
below),  is  the  lymphatic  or  adenoid  tissue,  also  called 
cytogenous  tissue.  Like  all  other  gland-tissue,  it 
is  supplied  with  a  rich  network  of  capillaries 
derived  from  an  afferent  artery,  and  leading  into 
efferent  veins. 

122.  The  elements  constituting  this  tissue  are  : — 

(a)  The  adenoid  reticulum  (Fig.  57),  a  network 
of  fine  homogeneous  fibrils,  with  numerous  plate-like 
enlargements. 

(b)  Small,  transparent,  fiat,  endotheloid  cell-plates, 
each  with  an  oval  nucleus.  These  cell-plates  are  fixed 
on  the  reticulum,  of  which  at  first  sight  they  seem 
to  form  part.  Their  oval  nucleus  especially  appears 
to  belong  to  a  nodal  point — i.e.,  to  one  of  the 
enlargements  of  the  reticulum ;  but  by  continued 
shaking  of  a  section  of  any  lymphatic  tissue,  the  oval 
nuclei  and  their  cell-plates  can  be  got  rid  of,  so  that  only 
the  reticulum  is  left,  without  any  trace  of  a  nucleus. 


Chap,  xii.]     Simple  Lymphatic  Glands. 


93 


^cMV. 


(c)  Lymph-corpuscles  completely  fill  the  meshes 
of  the  adenoid  reticulum.  These  can  be  easily 
shaken  out  of  the  reticulum.  They  are  of  dif- 
ferent sizes ; 
some  —  the 
young  ones — 
are  small  cells, 
with  a  com- 
paratively 
large  nucleus ; 
others  —  the 
ripe  ones — are 
larger,  have  a 
distinct  pro- 
toplasmic cell 
body,  with  one 
or  two  nuclei. 
They  all  show 
on  a  warm 
stage  amoe- 
boid move- 
ment, but  in 
the  large  ones 
it  is  much  more  pronounced  than  in  the  small  ones. 

The  capillary  blood-vessels  supplying  the  adenoid 
tissue  receive  a  more  or  less  distinct  special  investment 
from  the  adenoid  reticulum ;  this  is  the  capillary 
adventitia. 

123,  The  adenoid  tissue  occurs  as  : 

(1)  Diffuse  adenoid  tissue,  without  any  definite 
grouping  or  arrangement.  This  is  the  case  in  the  sub- 
epithelial layer  of  the  mucous  membrane  of  the  trachea, 
in  the  mucous  membrane  of  the  false  vocal  cords  and 
the  ventricle  of  the  larynx,  in  the  posterior  part  of 
the  epiglottis,  in  the  soft  palate  and  tonsils,  at  the 
root  of  the  tongue,  in  the  pharynx,  in  the  mucosa 
of  the  small  and  large  intestine,  including  the  villi 


Fier.  57. — Adenoid  Eeticulum  shaken  out ;  most  of 
the  Lymph-corpuscles  are  removed.     From  a 
Lymphatic  Gland, 
a,  The  reticulum ;  c,  a  capillary  blood-vessel.    (Atlas.) 


94 


Elements  of  Histology 


[Chap.  XII. 


of  the  former ;    and  in  the  mucous  membrane  of  the 
nasal  cavity  and  vagina. 

(2)  Cords,  cylinders,  or  patches  of  adenoid  tissue ; 
as  in  the  omentum  and  pleura,  and  in  the  spleen 
(Malpighian  corpuscles). 

(3)  Lymph  follicles,  i.e.,  oval  or  spherical  masses 
more  or  less  well  defined  ;  as  in  the  tonsils,  at  the  root 
of  the  tongue,  in  the  upper  part  of  the  pharynx  (pharynx- 
tonsil),  in  the  stomach,  small  and  large  intestine ;  in 
the  nasal  mucous  membrane,  in  the  large  and  small 
bronchi ;  and  in  the  spleen  (Malpighian  corpuscles). 

124.  The  tonsils  (Fig.  58)  are  masses  of  lymph  folli- 
cles and  diffuse  adenoid  tissue  covered  with  a  thin  mucous 
membrane,  which  penetrates  in  the  shape  of  longer  or 


/'  ~-i%@mim^     -7T7 

Fig.  58.— Vertical  Section  through  part  of  the  Tonsil  of  Dog. 

e,  Stratified  pavement,  epithelium  covering  tlie  free  surface  of  the  raucous 
membrane.  The  tissue  of  the  mucous  membrane  is  infiltrated  with  adenoid 
tissue.   /,  lymph  follicles ;  m,  mucous  gland  of  the  submucous  tissue.   (Atlas.) 


chap,  xii.]     Simple  Lymphatic   Vessels.  95 

shorter  folds  into  the  substance  within.  Numbers  of 
mucus-secreting  glands  situated  outside  the  layer  of 
lymph  follicles  discharge  their  secretion  into  the  pits — 
the  crypts — between  the  folds.  The  free  surface  of  the 
tonsils  and  the  crypts  is  covered  or  lined  respectively 
with  the  same  stratified  epithelium  that  lines  the  oral 
cavity.  Numbers  of  lymph  corpuscles  constantly,  in 
the  perfectly  normal  condition,  migrate  through  the 
epithelium  on  to  the  free  surface,  and  are  mixed  with 
the  secretions  (mucus  and  saliva)  of  the  oral  cavity. 
The  so-called  mucous  or  salivary  corpuscles  of  the 
saliva,  taken  from  the  oral  cavity,  are  such  discharged 
lymph  corpuscles.  They  become  swollen  up  by  the 
water  of  the  saliva,  and  assume  a  spherical  shape. 
They  finally  disintegrate. 

Similar  relations,  only  on  a  smaller  scale,  obtain 
at  the  root  of  the  tongue. 

The  'pharynx  tonsil  of  Luschka,  occurring  in  the 
upper  part  of  the  pharynx,  is  in  all  essential  respects 
the  same  as  the  palatine  tonsil.  Owing  to  large  parts 
of  the  mucous  membrane  of  the  upper  portion  of  the 
pharynx  being  covered  with  ciliated  columnar  epithe- 
lium, some  of  the  crypts  in  the  pharynx  tonsil  are  also 
lined  with  it. 

125.  The  lenticular  glands  of  the  stomach  are 
single  lymph  follicles. 

The  solitary  glands  of  the  small  and  especially 
the  large  intestine  are  single  lymph  follicles. 

The  agminated  glands  of  the  ileum  are  groups 
of  lymph  follicles.  The  mucous  membrane  containing 
them  is  much  thickened  by  their  presence,  and  repre- 
sents a  Peyer's  patch  or  a  Peyer's  gland. 

126.  In  most  instances  the  capillary  blood-vessels 
form  in  the  lymph  follicles  meshes,  arranged  in  a  more 
or  less  radiating  manner  from  the  periphery  towards 
the  centre ;  around  the  periphery  there  is  a  network 
of  small  veins.      A  larger  or  smaller  portion  of  the 


96  Elements  of  Histology.       [chap.  xn. 

circumference  of  the  follicles  of  the  tonsils,  pharynx, 
intestine,  bronchi,  &c,  is  surrounded  by  a  lymph 
sinus  leading  into  a  lymphatic  vessel.  The  lymphatic 
vessels  and  lymph  sinuses  in  the  neighbourhood  of  lym- 
phatic follicles  or  of  diffuse  adenoid  tissue  are  almost 
always  found  to  contain  numerous  lymph  corpuscles, 
thus  indicating  that  these  are  produced  by  the  adenoid 
tissue  and  absorbed  by  the  lymphatics. 

127.  The  Thymus  gland  consists  of  a  frame- 
work and  the  gland  substance.  The  former  is  fibrous 
connective  tissue  arranged  as  an  outer  capsule,  and 
in  connection  with  it  are  septa  and  trabecular  passing 
into  the  gland  and  subdividing  it  into  lobes  and 
lobules,  which  latter  are  again  subdivided  into  the 
follicles  (Fig.  59a).  The  follicles  are  very  irregular 
in  shape,  most  of  them  being  oblong  or  cylindrical 
streaks  of  adenoid  tissue.  Near  the  capsule  they  are 
well  defined  from  one  another,  and  present  a  poly- 
gonal outline ;  farther  inwards  they  are  more  or  less 
fused.  Each  shows  a  central  transparent  medulla 
and  a  peripheral  less  transparent  cortex  (Watney). 
At  the  places  where  two  follicles  are  fused  with  one 
another  the  medulla  of  both  is  continuous.  The  matrix 
is  adenoid  reticulum,  the  fibres  of  the  medullary  part 
being  coarser  and  shorter,  those  of  the  cortical  portion 
of  the  follicle  finer  and  longer.  The  meshes  of  the 
of  the  reticulum  in  the  cortical  part  of  the  follicles  are 
filled  with  the  same  lymph-corpuscles  as  occur  in  the 
adenoid  tissue  of  other  organs,  but  in  the  medullary 
part  they  are  fewer,  and  the  meshes  are  more  or  less 
completely  occupied  by  the  enlarged  but  transparent 
endotheloid  plates.  These  conditions  cause  the  greater 
transparency  of  the  medulla.  In  some  places  the 
endotheloid  cells  are  granular,  and  include  more  than 
one  nucleus  ;  some  are  even  multinucleated  giant  cells. 

128.  There  occur  in  the  medulla  of  the  follicles, 
larger  or  smaller,  more  or  less  concentrically-arranged 


chap,  xii.]     Simple  Lymphatic  Glands. 


97 


nucleated  protoplasmic  cells,  which  are  the  concentric 
bodies  of  Hassall  (Fig.  59b).     They  are  met  with  al- 


Fig.  59a.— Section  through,  the  Thymus  Gland  of  a  Foetus. 

a,  Fibrous  tissue  between  the  follicles ;  6,  the  cortical  portion  of  the  follicles ; 
c,  the  medullary  portion. 

ready  in  the  early  stages  of  the  life  of  the  thymus,  and 
cannot  therefore  be  connected  with  the  involution  of 
the  gland,  as  maintained  by  Afanassief,  according  to 
whom  the  concentric  cor- 
puscles    are    formed    in 
blood-vessels  which  there- 
by   become     obliterated. 
According     to     Watney 
they  are  concerned  in  the 
formation  of  blood-vessels 
and  connective  tissue. 

The  lymphatics  of  the 
interfollicular   septa   and   trabecule   always    contain 
numbers  of  lymph  corpuscles.      The  blood  capillaries 
of   the  follicles   are   more   richly  distributed  in  the 


Fig.  59b. — Two  Concentric  or  Has- 
sall's  Corpuscles  of  the  Thymus. 
Foetal  Gland. 


98  Elements  of  Histology.      [Chap.  xm. 

cortex  tlian  in  the  medulla,  and  they  radiate  from  the 
periphery  towards  the  central  parts. 

129.  After  birth,  the  thymus  gland  commences  to 
undergo  degeneration,  leading  to  the  gradual  dis- 
appearance of  the  greater  portion  of  the  gland,  its 
j)lace  being  taken  by  connective  tissue  and  fat.  But 
the  time  when  the  involution  is  completed  varies 
within  very  broad  limits. 

It  is  not  unusual  to  find  in  individuals  of  fifteen 
to  twenty  years  of  age  still  an  appreciable  amount  of 
thymus  gland  tissue.  In  some  animals — e.g.,  guinea- 
pigs — the  involution  of  the  gland  even  in  the  adult  has 
not  made  much  progress.  In  the  thymus  of  the  dog 
Watney  found  cysts  lined  with  ciliated  epithelial  cells. 


CHAPTER  XIII. 

COMPOUND     LYMPHATIC     GLANDS. 

1 30.  The  compound  or  true  lymphatic  glands  are 
directly  interpolated  in  the  course  of  lymphatic  vessels. 
Such  are  the  mesenteric,  portal,  bronchial,  splenic, 
sternal,  cervical,  cubital,  popliteal,  inguinal,  lumbar, 
tea,  glands.  Afferent  lymphatic  vessels  anastomosing 
into  a  plexus  open  at  one  side  (in  the  outer  capsule) 
into  the  lymphatic  gland,  and  at  the  other  (the  hilum) 
emerge  from  it  as  a  plexus  of  efferent  lymphatic  tubes. 

131.  Each  true  lymphatic  gland  is  enveloped  in  a 
fibrous  capsule  which  is  connected  with  the  interior 

and  the  hilum  by  connective  tissue  trabecules  and  septa. 
The  trabecule  having  advanced  a  certain  distance, 
about  one-third  or  one-fourth,  in  a  manner  more  or 
less  radiating  towards  the  centre,  branch  into  minor 
trabecule,  which  in  the  middle  part  of  the  gland  anasto- 
mose with  one  another  so  as  to  form  a  plexus  with  small 


chap,  xiii.]     Compound  Lymphatic  Glands. 


99 


meshes.  Thus  the  peripheral  third  or  fourth  of  the 
gland  is  subdivided  by  the  septa  and  trabecule,  into 
relatively  large  spherical  or  oblong  compartments,  while 
the  middle  portion  is  made  up  of  relatively  small  cylin- 
drical or  irregularly-shaped  compartments  (Fig.  60). 
The  former  region  is  the  cortex,  the  latter  the  medulla  of 
the  gland.  The  compartments  of  the  cortex  anastomose 
with  one  another  and  with  those  of  the  medulla,  and 
these  latter  also  form  one  intercommunicating  system. 
The  fibrous  capsule,  the  septa  and  trabecule  are 
the  carriers  of  the  vascular  trunks ;  the  trabecular 
consist  of  fibrous  connective  tissue  and  of  a  certain 


Fig.  60.— From  a  Vertical  Section  through  a  Lymphatic  Gland,  the 
Lymphatics  of  which  had  been  injected. 

c,  The  outer  capsule,  with  lymphatic  vessels  in  section  ;  a,  the  cortical  lymph 
follicles;  around  them  are  the  cortical  lymph  sinuses;  6,  the  medullary; 
injected  lymph  sinuses  between  the  masses  of  adenoid  tissue.    (Atlas.) 


amount  of  non-striped  muscular  tissue,  which  is  con- 
spicuous in  some  animals — e.g.,  pig,  calf,  rabbit, 
guinea-pig — but  is  scarce  in  man. 

Sometimes  coarsely  granular  connective  tissue  cells 


IOO 


Elements  of  Histology.      [Chap.xin. 


(plasma  cells)  are  present  in  considerable  numbers  in 
the  trabecule. 

132.  The  compartments  contain  masses  of  adenoid 
tissue,  without  being  completely  filled  with  it ;  those 
of  the  cortex  contain  oval  or  spherical  masses — the 
lymph  follicles  of  the  cortex ;  those  of  the  medulla 
cylindrical  or  irregularly-shaped  masses — the  medullary 
cylinders.  The  former  anastomose  with  one  another 
and  with  the  latter,  and  the  latter  amongst  them- 
selves, a  condition  easily  understood  from  what  has 
been  said  above  of  the  nature  of  the  compartments 
containing  these  lymphatic  structures.     The  follicles 

and  medullary 
cylinders  consist 
of  adenoid  tissue 
of  exactly  the 
same  character  as 
that  described  in 
the  previous  chap- 
ter. And  this 
tissue  also  con- 
tains the  last  rami- 
fications of  the 
blood-vessels,  i.e., 
the  last  branches 
of  the  arteries,  a 
rich  network  of 
capillary  blood- 
vessels, and  the 
first  or  smaller 
branches  of  the 
veins.  The 

capillaries    and 
other   vessels    re- 
ceive    also     here 
an  adventitious  envelope  from  the  adenoid  reticulum. 

133.  The   cortical    follicles   and    the    medullary 


Fig.  61.— From  a  Section  through  a 
Lymphatic  Gland. 

c,  The  outer  capsule;  *,  cortical  lymph  sinus; 
a,  adenoid  tissue  of  cortical  follicle.  Numerous 
nuclei,  indicating  lymph  corpuscles.    (Atlas.) 


chap,  xiii.]     Compound  Lymphatic  Glands.        ioi 

cylinders  do  not  completely  fill  out  the  compartments 
made  for  them  by  the  capsule  and  trabecule  respec- 
tively, but  a  small  peripheral  zone  of  each  compart- 
ment is  left  free  ;  this  is  a  lymphatic  sinus.  In  the 
cortex  it  is  spoken  of  as  a  cortical  (Fig.  61),  in  the 
medulla  as  a  medullary,  lymph  sinus  (Fig.  62).     The 


Fig.  62.— From  a  Section  through  the  Medulla  of  a  Lymphatic  Gland. 


a,  Transition  of  the  medullary  cylinders  of  adenoid  tissue  into  the  cortical 
follicles :  6,  the  lymph  sinuses  occupied  by  a  reticulum  ;  c,  the  fibrous  tissue 
trabecular ;  d,  the  medullary  cylinders.    (Atlas.) 

former  is  a  space  between  the  outer  surface  of  the 
cortical  lymph  follicle  and  the  corresponding  part  of 
the  capsule  or  cortical  septum,  the  latter  between  the 
surface  of  a  medullary  cylinder  and  the  trabecular. 
From  what  has  been  said  of  the  relation  of  the  com- 
partments, it  follows  that  the  cortical  and  medullary 
lymph  sinuses  form  one  intercommunicating  system. 


102  Elements  of  Histology.       [ChaP.xni. 

These  are  not  empty  free  spaces,  but  are  filled  with  a 
coarse  reticulum  of  fibres,  much  coarser  than  the  ade- 
noid reticulum  ;  to  it  are  attached  large  transparent 
cell  plates — endotheloid  plates.  In  some  instances  (as 
in  the  calf)  these  cell-plates  of  the  medullary  sinuses 
contain  brownish  pigment  granules,  which  give  to  the 
medulla  of  the  gland  a  dark  brown  aspect.  In  the 
meshes  of  the  reticulum  of  the  sinuses  are  contained 
lymph  corpuscles,  the  majority  of  which  consist  of  a 
relatively  large  protoplasmic  body,  and  one  or  two 
nuclei ;  they  show  lively  amoeboid  movement;  a  few 
small  lymph  corpuscles  are  also  amongst  them. 

The  surface  of  the  trabecular  facing  the  lymph 
sinuses  is  covered  with  a  continuous  layer  of  endothe- 
lium (von  Recklinghausen),  and  a  similar  endothelial 
membrane,  but  not  so  complete,  can  be  made  out  on 
the  surface  of  the  cortical  follicles  and  the  medullary 
cylinders.  The  endotheloid  plates,  as  applied  to  the 
reticulum  of  the  sinuses,  are  stretched  out,  as  it  were, 
between  the  endothelial  membrane  covering  the  sur- 
face of  the  trabecular  on  the  one  hand  and  that 
covering  the  surface  of  the  follicles  and  cylinders  on 
the  other. 

In  the  mesenteric  gland  of  the  pig  the  distribution 
of  cortical  follicles  and  medullary  cylinders  is  almost 
the  reverse  from  that  of  other  glands  or  in  other 
animals. 

134.  The  afferent  lymphatic  vessels  having  entered 
the  outer  capsule  of  the  gland,  and  having  formed 
there  a  dense  plexus,  open  directly  into  the  cortical 
lymph  sinuses.  The  medullary  lymph  sinuses  lead 
into  lymphatic  vessels,  which  leave  the  gland  per 
hilum  as  the  efferent  vessels. 

Both  afferent  and  efferent  vessels  are  supplied 
with  valves. 

135.  The  course  of  the  lymph  through  a  lymphatic 
gland  is  then  simply  this — from  the  afferent  vessels, 


chap,  xiv.]  Nerve-fibres.  103 

situated  in  the  capsule,  into  the  cortical  lymph  sinuses, 
from  these  into  the  medullary  sinuses,  and  from  these 
into  the  efferent  lymphatics.  Owing  to  the  presence 
of  the  reticulum  in  the  sinuses  the  current  of  the 
lymph  will  proceed  only  very  slowly  and  with  diffi- 
culty, as  if  it  were  passed  through  a  spongy  filter. 
Hence  a  large  number  of  formed  corpuscles,  pigment, 
inflammatory  or  other  elements,  passing  into  the  gland 
by  the  afferent  vessels  are  easily  arrested  and  de- 
posited in  the  sinuses,  and  there  readily  swallowed  by 
the  amoeboid  corpuscles  lying  in  the  meshes. 

Passing  a  stream  of  water  through  the  gland,  the 
contents  of  the  meshes  of  the  reticulum  of  the  sinuses — 
i.e.,  the  lymph  corpuscles — are  of  course  the  first  things 
washed  out  (von  Recklinghausen),  and  on  continuing 
the  stream  some  of  the  lymph  corpuscles  of  the 
follicles  and  cylinders  are  also  washed  out.  Hence  it 
is  probable  also  that  by  the  normal  stream  of  lymph 
passing  through  the  gland,  lymph  corpuscles  are 
drained,  as  it  were,  from  the  follicles  and  cylinders 
into  the  sinuses.  The  amoeboid  movement  of  the  lymph 
corpuscles,  especially  of  the  large  and  ripe  ones,  will 
greatly  facilitate  their  passage  from  the  follicles  and 
cylinders  into  the  lymph  sinuses. 


CHAPTER  XIV. 

NERVE-FIBRES. 

136.  The  nerve-fibres  conduct  impulses  to  or  from 
the  tissues  and  organs  on  the  one  hand,  and  the  nerve- 
centres  on  the  other,  and  accordingly  we  have  to  con- 
sider in  each  nerve-fibre  the  peripheral  and  central 
termination  and  the  conducting  part.     The  latter,  i.e., 


104 


Elements  of  Histology.       [Chap.  xiv. 


the  nerve-fibres  proper,  in  the  cerebro-spinal  nerves  are 
grouped  into  bundles,  and  these  again  into  anatomical 
nerve-branches  and  nerve-trunks.  Each  anatomical 
cerebro-spinal  nerve  consists,  therefore,  of  bundles  of 
nerve-fibres  (Fig.  63).  The  general  matrix  by  which 
these  bundles  are  held  together  is  fibrous  connective 
tissue  called  the  Epineurium  (Key  and  Retzius) ;  this 
epineurium  is  the  carrier  of  the  larger  and  smaller 
blood-vessels  with  which  the  nerve-trunk  is  supplied, 
of  a  plexus  of  lymphatics,  of  groups  of  fat-cells,  and 
sometimes  of  numerous  plasma  cells. 

137.  The  nerve-bundles  (Fig.  64)  are  of  various  sizes, 
according  to  the  number  and  size  of  the  nerve-fibres  they 
contain.     They  are  well-defined  by  a  sheath  of  their 


Fig.  63. — From  a  Transverse   Section  through  the   Sciatic  Nerve  of 

the  Dog. 

ep,  Epineurium ;   p,  perineurium  ;  n,  nerve  fibres  constituting  a  nerve-bundle  iD 

cross  section  ;  /,  fat  tissue  surrounding  the  nerve.    (Atlas.) 

own,  called  perineurium  (Key  and  Hetzius).  This  peri- 
neurium consists  of  bundles  of  fibrous  connective  tissue 
arranged  in  lamellae,  every  two  lamellae  being  separated 
from  one  another  by  smaller  or  larger  lymph  spaces, 


Chap,  xiv.]  Nerve-fibres.  105 

which  form  an  intercommunicating  system,  and 
anastomose  with  the  lymphatics  of  the  epineurium 
whence  they  can  be  injected.  Between  the  lamellae, 
and  in  the  spaces,  are  situated  flattened  endotheloid 
connective  tissue  corpuscles. 

The  nerve-bundles  are  either  single  or  compourid. 
In  the  former  the  nerve-fibres  contained  in  a  bundle 
are  not  sub-divided  into  groups,  in  the  latter  the 
bundles  are  sub-divided  by  thicker  and  thinner  septa 
of  fibrous  connective  tissue  connected  with  the  peri- 
neurium. When  a  nerve-bundle  divides — as  when  a 
trunk  repeatedly  branches,  or  when  it  enters  on  its  peri- 
pheral distribution — each  branch  of  the  bundle  receives 
a  continuation  of  the  lamellar  perineurium.  The  more 
branches  the  perineurium  has  to  supply,  the  more  re- 
duced it  becomes  in  thickness.  In  some  of  these  minute 
branches  the  perineurium  is  reduced  to  a  single  layer 
of  endothelial  cells.  When  one  of  these  small  bundles 
breaks  up  into  the  single  nerve-fibres,  or  into  small 
groups  of  them,  each  of  these  has  also  a  continuation 
of  the  fibrous  tissue  of  the  perineurium.  In  some 
places  this  jjerineural  continuation  is  only  a  very 
delicate  endothelial  membrane,  at  others  it  is  of 
considerable  thickness,  and  still  shows  the  laminated 
nature.  Such  thick  sheaths  of  single  nerve-fibres, 
or  of  small  groups  of  them,  represent  what  is  called 
Henle's  sheath. 

138.  The  nerve-fibres  are  held  together  within  the 
bundle  by  connective  tissue,  called  the  Endoneurium 
(Fig.  64).  This  is  a  homogeneous  ground  substance  in 
which  are  embedded  fine  bundles  of  fibrous  connective 
tissue,  and  connective  tissue  corpuscles,  and  capillary 
blood-vessels  arranged  so  as  to  form  a  network  with 
elongated  meshes.  Between  the  perineurium  and  the 
nerve-fibres  are  found  here  and  there  lymph  spaces ; 
similar  spaces  separate  the  individual  nerve-fibres,  and 
have  been  injected  by  Key  and  Retzius. 


io6 


Elements  of  Histology.       [Chap.  xiv. 


When  nerve-trunks  anastomose  so  as  to  form  a 
plexus — e.g.,  in  the  brachial,  or  sacral  plexus — there 
occurs  an  exchange  and  re- arrangement  of  nerve- 
bundles  in  the  branches.  A  similar  condition  obtains 
in  the  ganglia  of  the  cerebro-spinal  nerves.     Nerve- 


Pig.    64. — Transverse    Section   through   a   Nerve-bundle 
in  the  Tail  of  Mouse. 

P,  The  perineurium  ;  e,  the  endoneurium  separating  the  medullated  nerve-fibres 
seen  in  cross  section  ;  I,  lymph  spaces  in  the  perineurium  ;  V,  lymph  spaces 
in  the  endoneurium.    (Atlas.) 


trunks  and  nerve-branches  passing  through  a  lymph 
cavity,  such  as  the  subdural  spaces,  or  the  sub- 
cutaneous lymph  sacs,  or  the  cisterna  lymphatica 
magna  in  the  frog,  receive  from  the  serous  membrane 
an  outer  endothelial  covering. 

139.  The  nerve-fibres  in  the  nerve-bundles  of  the 
cerebro-spinal  nerves,  with  the  exception  of  the 
olfactory  nerve,  are  medullated  nerve-fibres.  These  are 
doubly  or  darkly  contoured  smooth  cylindrical  fibres, 
varying  in  diameter  between  ytjVo"  an(^  tufotj"  °^  an 
inch.  Within  the  same  bundle  of  a  nerve — e.g.,  of 
the  brachial  or  sacral  plexus — there  occur  fibres  which 
are  several  times  thicker  than  others,  and  it  is  pro- 
bable that  they  are  derived  from  different  sources. 
Schwalbe  has  shown  that  the  thickness  of  the  nerve- 


Chap.  XIV.]  Nf.R  VE-FIBR  ES.  I O  7 

fibre  stands  in  a  certain  relation  to  the  distance  of  its 
periphery  from  the  nerve-centre  and  to  functional 
activity. 

A  medullated  nerve-fibre  in  the  fresh  condition 
is  a  bright  glistening  cylinder,  showing  a  dark 
double  contour.  Either  spontaneously  after  death, 
or  after  re-agents — as  water,  salt  solution,  dilute 
acids — or  after  pressure  and  mechanical  injury,  the 
outline  of  the  nerve-fibre  becomes  irregular ;  smaller, 
or  larger,  glistening  dark-bordered  droplets  and  masses 
appear  and  gradually  become  detached.  These 
droplets  and  masses  are  derived  from  the  fatty  sub- 
stance constituting  the  medullary  sheath  or  white 
substance  of  Schwann  (see  below).  When  a  nerve- 
fibre  within  the  bundle  undergoes  degeneration  during 
life,  either  after  section  of  the  nerve  or  after  other 
pathological  changes,  or  in  the  natural  course  of  its 
existence  (S.  Mayer),  the  medullary  sheath  breaks  up 
into  similar  smaller  or  larger  globules  or  particles, 
which  gradually  become  absorbed. 

140.  Each  medullated  nerve-fibre  (Figs.  64a,  Q6) 
consists  of  the  following  parts  :  (a)  the  central  axis 
cylinder.  This  is  the  essential  part  of  the  fibre,  and  is 
a  cylindrical  or  bandlike,  pale,  transparent  structure, 
which  in  certain  localities  (near  the  terminal  distribu- 
tion, in  the  olfactory  nerves,  in  the  central  nervous 
system),  and  especially  after  certain  re-agents,  shows 
itself  composed  of  very  fine  homogeneous  or  more  or 
less  beaded  fibrillse — the  elementary  or 'primitive  fibrillar 
(Max  Schultze) — held  together  by  a  small  amount  of  a 
faintly  granular  interstitial  substance.  The  longitu- 
dinal striation  of  the  axis  cylinder  is  due  to  its  being 
composed  of  primitive  fibrillse.  The  thickness  of  the 
axis  cylinder  is  in  direct  proportion  to  the  thickness 
of  the  whole  nerve-fibre.  The  axis  cylinder  is  said 
to  be  enveloped  in  its  own  hyaline  more  or  less  elastic 
sheath,  composed  of  neurokeratin. 


io8 


Elements  of  Histology.       [Chap.  xiv. 


141.  (6)  The  medullary  sheath  or  white  substance 
of  Schwann,  also  called  the  medulla  of  the  nerve-fibre. 
This  is  a  glistening  bright  fatty  substance  surrounding 
the  axis  cylinder,  as  an  insulating  hollow  cylinder 
surrounds  an  electric  wire.  The  medullary  sheath 
gives  to  the  nerve-fibre  its  double  or  dark  contour. 
Between  the  axis  cylinder  and  the  medullary  sheath 
there  is  a  small  amount  of  albuminous  fluid 
which  appears  greatly  increased 
when  the  former,  owing  to  shrink- 
ing, stands  farther  apart  from  the 
latter. 

142.  (c)  The  sheath  of  Schwann, 
or  the  neurilemma,  surrounds  closely 
the  medullary  sheath,  and  forms 
the  outer  boundary  of  the  nerve- 
fibre.  It  is  a  hyaline  delicate 
membrane.  From  place  to  place 
there  is  present  between  the  neuri- 
lemma and  the  medullary  sheath,  and 
situated  in  a  depression  of  the  latter, 
an  oblong  nucleus,  surrounded  by  a 
thin  zone  of  protoplasm.  These 
nucleated  corpuscles  are  the  nerve 
corpuscles  (Fig.  64a),  and  are  analo- 
gous to  the  muscle  corpuscles,  situated 
between  the  sarcolemma  and  the 
striated  muscular  substance.  They 
are  not  nearly  so  numerous  as  the 
muscle  corpuscles. 

143.  The  neurilemma  produces 
at  certain  definite  intervals  annular 

constrictions,  the  nodes  or  constrictions  ofRanvier  (Figs. 
64a,  65, 66),  and  at  these  nodes  of  Ranvier  the  medullary 
sheath,  but  not  the  axis  cylinder  and  its  special  sheath, 
suffers  a  discontinuity  and  sharply  terminates.  The 
portion  of  the  nerve-fibre  situated  between  two  nodes  is 


Ficr.  64a.— Two  Nerve 
Fibres,  showing  the 
nodes  or  constric- 
tions of  Ranvier  and 
the  axis  cylinder. 
The  medullary 
Bheath  has  been  dis- 
solved away.  The 
deeply  -  stained  ob- 
long nuclei  indicate 
the  nerve  corpuscles 
■within  the  neuri- 
lemma.   (Atlas.) 


Chap.  XIV.] 


Nerve-fibres. 


109 


the  internodal  segment.  Each  internodal  segment  has 
generally  one,  occasionally  more  than  one,  nerve 
corpuscle.  The  medul- 
lary cylinder  of  each  in- 
ternodal segment  is  made 
up  of  a  number  of  coni- 
cal sections  (Fig.  66a) 
imbricated  at  their  ends 
(Schmidt,  Lantermann) 
(Fig.  66),  and  each  such 


Fig.   66.— Medullated  Nerve- 
fibres. 

A,  A  medullated  nerve  -  fibre, 
showing  the  subdivision  of  the 
medullary  sheath  into  cylin- 
drical sections  imbricated  with 
their  ends ;  a  nerve  corpuscle 
with  an  oval  nucleus  is  seen 
between  the  neurilemma  and 
the  medullary  sheath  ;  b,  a 
medullated  nerve  fibre  at  a 
node  or  constriction  of  Ranvier; 
the  axis  cylinder  passes  unin- 
terruptedly from  one  segment 
into  the  other,  but  the  medul- 
lary sheath  is  interrupted. 
(.Key  and  Retzius.) 


Fig.    65.  —  Medullated   Nerve  -  fibres, 
after  staining  with  Nitrate  of  Silver. 

a,  The  axis  cylinder ;  &,  Ranvier's  constric- 
tion.   (Key  and  Retzius.) 


section  is  again  made  up  of 
a  large  number  of  rod-like 
structures  (Fig.  67)  placed 
vertically  on  the  axis  cylin- 
der. 

These  rods  are,  how- 
ever, connected  into  a  net- 
work. The  network  itself 
is  very  likely  the  neuro- 
keratin of  Ewald  and  Kuhne, 
whereas  the  interstitial  sub- 
stance of  the  network  is 
probably  the  fatty  sub- 
stance leaving  the  nerve- 
fibre  in  the  shape  of  droplets 


no 


Elements  of  Histology.       [Chap.  xiv. 


when  pressure  or  reagents  are  applied  to  the  fresh 
nerve-fibre. 

144.  Medullated  nerve-fibres  without  any  neuri- 
lemma, and  consequently  without  any  nodes  of  Ranvier, 
with  a  thick  more  or  less  distinctly  laminated  medul- 
lary sheath,  form  the 
white  substance  of  the 
brain  and  spinal  cord. 
In  these  organs,  in  the 
hardened  and  fresh  state, 
numerous  nerve  -  fibres 
may  be  noticed,  which 
show  more  or  less  regu- 
lar varicosities,  owing  to 
local  accumulations  of 
fluid  between  the  axis 
cylinder  and  medullary 
sheath.  These  are  called 
varicose  nerve-fibres. 
They  occur  also  in  the 
branches  of  the  sympa- 
thetic nerve. 

The  nerve-fibres  of 
the  optic  and  acoustic 
nerve  are  medullated, 
but  without  any  neuri- 
lemma ;  varicose  fibres 
are  common  in  them. 

145.  Medullated 
nerve-fibres  occasionally 
in  their  course  divide  into  two  medullated  fibres.  Such 
division  is  very  common  in  medullated  nerve-fibres 
supplying  striped  muscular  fibres,  especially  at  or  near 
thepointof  entrance  into  the  muscular  fibres  (see  below). 
But  also  in  other  localities  division  of  nerve-fibres 
may  be  met  with.  The  electric  nerve  of  the  electric 
fishes    (malapterurus,    gymnotus,    silurus,   etc.,    elec- 


Fig.  67.— Medullated  Nerve-fibres. 

A,  B,  showing  on  a  surface  view  the 
reticulated  nature  of  the  medullary 
sheath  ;  c,  two  nerve-fibres  showing 
the  axis  cylinder,  the  medullary  sheath 
with  their  vertically-arranged  minute 
rods,  and  the  delicate  neurilemma  or 
outer  hyaline  sheath.    (Atlas.) 


chap,  xiv.]  Nerve-fibres.  t  r  i 

tricus)  shows  such  divisions  to  an  extraordinary  degree, 
one  huge  nerve-fibre  dividing  at  once  into  a  bundle  of 
minor  fibres.  Division  of  a  medullated  fibre  takes 
place  generally  at  a  node  of  Ranvier.  The  branches 
taken  together  are  generally  thicker  than  the  un- 
divided part  of  the  fibre,  but  in  structure  they  are  iden- 
tical with  the  latter. 

146.  When  medullated  nerve-fibres  approach  their 
peripheral  termination,  they  change  sooner  or  later,  in 
so  far  as  their  medullary  sheath  suddenly  ceases ;  and 
now  we  have  a  non-medullated,  or  Remak's  nerve- 
fibre.  Each  of  these  consists  of  an  axis  cylinder,  a 
neurilemma,  and  between  the  two  a  nucleated  nerve 
corpuscle  from  place  to  place.  Non  -medullated  nerve- 
fibres  always  show  the  fibrillar  nature  of  their 
axis  cylinder.  The  olfactory  nerve-branches  are 
entirely  made  up  of  non-medullated  nerve -fibres.  In 
the  branches  of  the  sympathetic  most  fibres  are  non- 
medullated. 

The  non-medullated  fibres  undergo  always  repeated 
divisions.  They  form  plexuses,  large  fibres  branching 
into  smaller  ones,  and  these  again  joining  (Fig.  68). 
Generally  at  the  nodal  points  of  these  plexuses  there  are 
triangular  nuclei,  indicating  the  corpuscles  of  the 
neurilemma. 

147.  Finally  the  non-medullated  nerve-fibres  lose 
their  neurilemma,  and  then  we  have  simple  axis 
cylinders.  These  branch  and  ultimately  break  up 
into  the  constituent  primitive  nerve-fibrillce,  which 
occasionally  show  regular  varicosities  (Fig.  69). 
Of  course,  of  a  neurilemma  or  the  nuclei  of  the 
nerve  corpuscles  there  is  nothing  left.  These 
primitive  fibrillse  branch  and  anastomose  with  one 
another,  and  thus  form  a  network.  The  density 
of  this  network  depends  on  the  number  of  primitive 
fibrils  and  the  richness  of  their  branch  inar.  These 
primitive   fibrils    and    their    networks  represent   the 


112 


Elements  of  Histology.       [chap.  xiv. 


peripheral  termination,  and  this  mode  of  termination 
occurs  in  the  nerve-fibres  of  common  sensation,  as  in 
many  of   the  nerve-fibres  of   the  skin,   cornea,    and 


Fig.  68. — Plexus  of  Fine  Non-medullated  Nerve-fibres  of  the  Cornea. 

a,  A  thick non-medullated  nerve-fibre:  6,  a  fine  one;  c,  d,  elementary  fibrils, 
anastomosing  into  a  network. 

mucous  membranes.  In  all  these  cases  the  peripheral 
termination,  i.e.,  the  primitive  fibrils  and  their  net- 
works are  found  intra-epithelial  (Fig.  70),  i.e.  situated 
in  the  stratum  Malphigii  of  the  epidermis,  in  the  epithe- 
lial parts  of  the  hair  follicle,  in  the  anterior  epithelium 
of  the  cornea,  and  in  the  epithelium  of  the  mucous 


Chap.  XIV.] 


Ner  VE- FIB RES. 


113 


membranes.     The  primitive   nerve-fibrils   lie   in   the 
interstitial  substance  between  the  epithelial  cells,  as 


Fig.  69.— Nerve-fibres  of  the  Cornea. 

a,  An  axis  cylinder  splitting  up  into  its  constituent  primitive  fi brillae  near  the 
anterior  epithelium  of  the  cornea ;  6,  primitive  fibrillar. 


intra-epithelial  networks  and  as  primitive  fibrils  which 
appear  to  terminate  with  free  ends. 

148.  Tracing  then  a  nerve-fibre,  say  one  of  common 
sensation,  from  the  periphery  towards  the  centre,  we 
have  isolated  primitive  fibrils  or  networks  of  them ; 


ii4 


Elements  of  Histology.      [chap.  xiv. 


they  form  by  association  simple  axis  cylinders,  which 
vary  in  thickness  according  to  the  number  of  their 
constituent  primitive  fibrils.     These  simple  axiscylin- 


Fig.  70.— Intra-epithelial  Nerve -termination  in  the  Anterior  Epithelium 
.  of  the  Cornea,  as  seen  in  an  oblique  section. 

a,  An  axis  cylinder ;  b,  sub-epithelial  nerve-fibrillas ;  c,  intra-epithelial  network ; 
d,  epithelial  cells.    (Handbook.) 


ders  form  plexuses.  By  association  they  make  larger 
axis  cylinders,  and  these  becoming  invested  with  a 
neurilemma,  and  with  the  nuclei  of  nerve  corpuscles, 
form  non-medidlated  nerve-fibres.  These  also  form 
plexuses.  A  medullary  sheath  makes  its  appearance 
between  the  neurilemma  and  the  axis  cylinder,  and 
thus  forms  a  medullated  nerve-fibre. 


Chap.  XV.]  115 


CHAPTER  XV. 

PERIPHERAL    NERVE-ENDINGS. 

149.  In  the  preceding  chapter  the  termination  of 
the  nerves  of  common  sensation,  as  isolated  primitive 
fibrillEe,  and  as  networks  of  these,  has  been  described 
in  the  epithelium  of  the  skin  and  mucous  mem- 
branes, and  in  the  anterior  epithelium  of  the  cornea* 
Besides  these  there  are  other  special  terminal  organs 
of  sensory  nerves,  probably  concerned  in  the  per- 
ception of  some  special  quality  or  quantity  of  sensory 
impulses.  They  are  all  connected  with  a  meclullated 
nerve-fibre,  and  are  situated,  not  in  the  epithelium 
of  the  surface,  but  in  the  tissue,  at  greater  or 
lesser  depth.  Such  are  the  Pacinian  corpuscles,  the 
Herbst  corpuscles,  the  end-bulbs  of  Krause  in  the 
tongue  and  conjunctiva,  the  genital  end-corpuscles  or 
end-bulbs  in  the  external  genital  organs,  the  corpuscles 
of  Meissner,  or  tactile  corpuscles,  in  the  papillae  of 
the  skin  of  the  volar  side  of  the  fingers,  the  touch-cells 
of  Merkel  in  the  beak  and  tongue  of  duck,  &.c. 

150.  The  Pacinian  corpuscles.  —  These  are 
also  called  "Vater's  corpuscles.  They  occur  in  large 
numbers  on  the  subcutaneous  nerve-fibres  of  the  palm 
of  the  hand  and  foot  of  man,  in  the  mesentery  of  the 
cat,  along  the  tibia  of  the  rabbit,  on  the  genital  organs 
of  man  (corpora  cavernosa,  prostate).  Each  corpuscle 
is  oval,  more  or  less  pointed,  and  in  some  places 
easily  perceptible  to  the  unaided  eye  (palm  of 
the  human  hand,  mesentery  of  the  cat),  the  largest 
being  about  -^th  of  an  inch  long  and  -^-th  of  an  inch 
broad ;  in  other  places  they  are  of  microscopic  size 
only.     Each  possesses  a  stalk,  to  which  it  is  attached, 


n6 


Elements  of  Histology. 


[Chap.  xv. 


and  which  is  a  single  efferent  medullated  nerve-fibre 
(Fig.  71),  differing  from  an  ordinary  medullated  nerve- 
fibre  merely  in  the  fact  that  outside  the  neurilemma  of 

the  nerve-fibre  there  is 
present  a  thick  laminated 
connective  tissue  sheath, 
which  is  the  sheath  of 
Henle — continuous  with 
the  perineural  sheath  of 
the  nerve  branch  with 
which  the  nerve-fibre  is  in 
connection.  This  medul- 
lated nerve-fibre  within  its 
sheath  possesses  generally 
a  very  wavy  outline.  The 
corpuscle  itself  is  com- 
posed of  a  large  number  of 
lamellae,  or  capsules,  more 
or  less  concentrically  ar- 
ranged around  a  central 
elongated  or  cylindrical 
clear  sjiace.  This  space 
contains  in  its  axis  from 
the  proximal  end,  i.e.,  the 
one  nearest  to  the  stalk,  to 
near  the  opposite  or  distal 
end,  a  continuation  of  the  nerve-fibre  in  the  shape  of  a 
si?nple  axis  cylinder.  But  this  axis  cylinder  does  not 
fill  out  the  central  space,  since  there  is,  all  round  the 
faintly  and  longitudinally  striated  axis  cylinder,  a  good 
deal  of  space  left  filled  with  a  transparent  substance,  in 
which,  in  some  instances,  rows  of  spherical  nuclei  may 
be  perceived  along  the  margin  of  the  axis  cylinder. 
At  or  near  the  distal  end  of  the  central  space  the 
axis  cylinder  divides  in  two  or  more  branches,  and 
these  terminate  in  pear-shaped,  oblong,  spherical,  or 
irregularly -shaped  granu]ar-looking  enlargements. 


Fig.  71. — A  Pacinian  Corpuscle, 
from  the  Mesentery  of  the  Cat. 

a,  The  medullated  nerve-fibre ;  5,  the 
concentric  capsules. 


Chap,  xv.]     Peripheral  Nerve-endings.  117 

151.  The  concentric  capsules  forming  the  corpuscle 
itself  are  disposed  in  a  different  manner  at  the  periphery 
and  near  the  central  space  from  that  in  which  they 
are  disposed  in  the  middle  parts,  viz.,  in  the  former 
localities  they  are  much  closer  together,  being  thinner 
than  in  the  latter.  On  looking,  therefore,  at  a 
Pacinian  corpuscle  in  its  longitudinal  axis,  or  in  cross 
section,  we  always  notice  the  striation  (indicating  the 
capsules)  to  be  closer  in  the  former  than  in  the  latter 
places.  Each  capsule  consists  of — (a)  a  hyaline,  pro- 
bably elastic,  ground  substance,  in  which  are  embedded 
here  and  there  (b)  fine  bundles  of  connective  tissue 
fibres ;  (c)  on  the  inner  surface  of  each  capsule,  i.e., 
the  one  directed  to  the  central  axis  of  the  Pacinian 
corpuscle,  is  a  single  layer  of  nucleated  endothelial 
plates.  The  oblong  nuclei  visible  on  the  capsules  at 
ordinary  inspection  are  the  nuclei  of  these  endothelial 
plates.  There  is  no  fluid  between  the  capsules,  but 
these  are  in  contact  with  one  another  (Huxley). 
Neighbouring  capsules  are  occasionally  connected  with 
one  another  by  thin  fibres. 

152.  In  order  to  reach  the  central  space  of  the 
corpuscle,  the  medullated  nerve-fibre  has  to  perforate 
the  capsule  at  one  pole ;  thus  a  canal  is  formed 
in  which  is  situated  the  medullated  nerve-fibre, 
and  as  such,  and  in  a  very  wavy  condition,  it  reaches 
the  proximal  end  of  the  central  space.  This 
part  of  the  nerve-fibre  may  be  called  the  interme- 
diary part.  The  lamellse  of  the  sheath  of  Henle 
pass  directly  into  the  peripheral  capsules  of  the 
corpuscle. 

Immediately  before  entering  the  central  space,  the 
nerve-fibre  divests  itself  of  all  parts  except  the  axis 
cylinder,  which,  as  stated  above,  passes  into  the  central 
space  of  the  Pacinian  corpuscle.  In  some  cases  a 
minute  artery  enters  the  corpuscle  at  the  pole,  opposite 
to   the   one    for   the    nerve-fibre;    it   penetrates   the 


n8 


Elements  of  Histology. 


[Chap.  xv. 


peripheral    capsules,    and   supplies  them  with   a  few 

capillary  vessels. 

153.  The  corpuscles  of  Herbst  are  similar  to 

the  Pacinian  corpuscles,  with  this  difference,  that  they 

are  smaller  and  more  elongated,  that  the  axis  cylinder 
of  the  central  space  is  bordered  by 
a  continuous  row  of  nuclei,  and 
that  the  capsules  are  thinner  and 
more  closely  placed  (Fig.  72). 
This  applies  especially  to  those 
near  the  central  space,  and  here 
between  these  central  capsules  we 
miss  the  nuclei  indicating  the  en- 
dothelial plates.  Such  is  the  nature 
of  Herbst's  corpuscles  in  the  mucous 
membrane  of  the  tongue  of  the 
duck,  and  to  a  certain  degree  also 
in  those  of  the  rabbit,  and  in 
tendons. 

154.  The  tactile  corpus- 
cles, or  corpuscles  of  Meiss- 
uer,  occur  in  the  papillae  of  the 
corium  of  the  volar  side  of  the 
fingers  and  toes  in  man  and  ape ; 
they  are  oblong,  straight,  or 
slightly  folded.  In  man  they  are 
about   g4^  to  3~g  of  an  inch  long, 

and  ■w~  to  2TTo  °^  an  mcn 
broad.  They  are  connected 
with  a  medullated  nerve  fibre — generally  one,  occa- 
sionally, but  rarely,  two — with  a  sheath  of  Henle. 
The  nerve-fibre  enters  the  corpuscle,  but  usually 
before  doing  so  it  winds  round  the  corpuscle  as  a 
medullated  fibre  once  or  twice  or  oftener,  and  its 
Henle's  sheath  becomes  fused  with  the  fibrous  capsule 
or  sheath  of  the  tactile  corpuscle.  The  nerve-fibre 
ultimately  loses  its  medullary  sheath  and  penetrate* 


Fig.  72.  —  A  Herbst's 
Corpuscle,  from  the 
Tongue  of  Duck. 

a,  The  medullated  nerve- 
flbre  cut  away. 


Chap,  xv.]      Peripheral  Nerve-endings. 


119 


into  the  interior  of  the  corpuscle,  where  the  axis 
cylinder  branches  ;  its  branches  re- 
tain a  coiled  course  all  along  the 
tactile  corpuscle  (Fig.  73),  anastomose 
with  one  another,  and  terminate  in 
slight  enlargements,  pear-shaped  or 
cylindrical.  These  enlargements,  ac- 
cording to  Merkel,  are  touch  cells. 
The  matrix,  or  main  part  of  the 
tactile  corpuscle  consists,  besides  the 
fibrous  sheath  with  nuclei  and  numer- 
ous elastic  fibres,  of  fine  bundles  of 
connective  tissue,  and  of  a  number 
of  nucleated  small  cells.  Fig.  73.— A  Tactile 

•11-1-        mi  a       «.'      ■ -^  *■      Corpuscle  ot  Meiss- 

155.     The    end- bulbs    of     ner  from  the  Skin  of 
firanse.- These  occur  in  the  con-     the  Human  Hand. 

,  •  p  in  i  i  Showing  the    convolu- 

iunctiva  01   call    and  man,   and   are     tions  of  the  uerve- 

t  1  t      i    •      i  j.  fibre.   (E.Fischer and 

oblong  or  cylindrical  minute  corpus-      w.  Fiemming.) 

cles  situated  in  the  deeper  layers  of 

the  conjunctiva, 
near  the  corneal 
margin.  A  medul- 
lated  nerve  -  fibre, 
with  Henle's  sheath, 
enters  the  corpuscle 
(Fig.  74).  This 
possesses  a  nu- 
cleated capsule,  and 
is  a  more  or  less 
laminated  (in  man 
more  granular- 
looking)  structure, 
numerous  nuclei  be- 
ing scattered  be- 
tween the  laminae. 
Of    the    nerve-fibre, 

a,  Medullated  nerve-fibre  ;  6,  the  capsule  of  the      ^g    ^    j;\\\q      Olllv    the 


Fig.  74.— An  End-bulb  of  Krause. 


120 


Elements  of  Histology, 


[Chap.  xv. 


axis  cylinder  is  prolonged  into  the  interior  of  the 
corpuscle.  Occasionally  the  medullated  nerve-fibre 
passes,  as  such,  into  the  corpuscle,  being  at  the 
same  time  more  or  less  convoluted.  Having  passed 
to  near  the  distal  extremity,  it  branches,  and  termi- 
nates with  small  enlargements  (Krause,  Longworth, 
Merkel,  Key  and  Retzius). 

The  end-bulbs  in  the  genital  organs,  or  the  genital 
corpuscles  of  Krause,  are  similar  in  structure  to  the 
simple  end-bulbs.  They  occur  in  the  tissue  of  the 
cutis  and  mucous  membrane  of  the  penis,  clitoris,  and 
vagina. 

156.  The  corpuscles  of  Granary  or  touch- 
corpuscles  of  Merkel,  in  the  tissue  of  the  papillae  in  the 
beak  and  tongue  of  birds,  are  oval  or  spherical  cor- 
puscles of   minute  size,  possessed  of  a  very  delicate 


•u       A  B       N^  C 

Fig.  75. — Corpuscles  of  Grandry  in  the  Tongue  of  Duck. 

a,  Composed  of  three  cells;  b,  composed  of  two  cells;  o,  showing  the  develop- 
ment of  a  Grandry's  corpuscle  from  the  epithelium  covering  the  papilla; 
e,  epithelium ;  n,  nerve-fibre.    (Izquierdo.) 


nucleated  membrane  as  a  capsule,  and  consisting  of  a 
series  (two,  three,  four,  or  more)  of  large,  slightly- 
flattened,  granular-looking,  transparent  cells,  each  with 
a  spherical  nucleus,  and  arranged  in  a  vertical  row  (Fig. 
75).  A  medullated  nerve-fibre  enters  the  corpuscle  from 
one  side,  and  losing  its  medullary  sheath,  the  axis  cy- 
linder branches,  and  its  branchlets  terminate,  according 
to  some  (Merkel,  Henle),  in  the  cells  of  the  corpuscle 


Chap,  xv.]     Peripheral  Nerve-endings.  121 

(touch-cells  of  Merkel)  ;  according  to  others  (Key  and 
Retzius,  Ranvier,  Hesse,  Izquierdo),  in  the  trans- 
parent substance  between  the  touch-cells,  thus  form- 
ing the  '  disc  tactil '  of  Ranvier  or  the  Tastplatte  of 
Hesse.  Neither  theory  seems  to  me  to  answer  to  the 
facts  of  the  case,  since  I  find  that  the  branchlets  of 
the  axis  cylinder  terminate,  not  in  the  touch-cells,  nor 
as  the  disc  tactil,  but  with  minute  swellings  in  the 
interstitial  substance  between  the  touch-cells,  in  a 
manner  very  similar  to  what  is  the  case  in  the  con- 
junctival end  bulbs.  According  to  Merkel,  single  or 
small  groups  of  touch-cells  occur  in  the  tissue  of -the 
papillae,  and  also  in  the  epithelium,  in  the  skin  of 
man  and  mammals. 

157.  In  articulations — e.g.,  the  knee-joint  of  the 
rabbit — Nicoladoni  described  numerous  nerve  branches, 
from  which  fine  nerve-fibres  are  given  off.  Some  of 
these  terminate  in  a  network,  others  on  blood-vessels, 
and  a  third  group  enter  Pacinian  corpuscles.  Krause 
described  in  the  synovial  membranes  of  the  joints  of 
the  human  fingers  medullated  nerve-fibres  which  end 
in  peculiar  tactile  corpuscles,  called  by  him  "  articula- 
tion-nerve corpuscles/' 

158.  The  nerve  branches  supplying*  non- 
striped  muscular  tissue  are  derived  from  the 
sympathetic  system.  They  are  composed  of  non- 
medullated  fibres,  and  the  branches  are  invested  in 
an  endothelial  sheath, — perineurium.  The  branches 
divide  into  single  or  small  groups  of  axis  cylinders, 
which  reunite  into  a  plexus — the  ground  plexus  of 
Arnold.  Small  fibres  coming  off  from  the  plexus 
supply  the  individual  bundles  of  non-striped  muscle 
cells,  and  they  form  a  plexus  called  the  intermediary 
plexus  (Fig.  76).  The  fibres  joining  this  plexus  are 
smaller  or  larger  bundles  of  primitive  fibrillse ;  in 
the  nodes — i.e.,  the  points,  of  meeting  of  these  fibres 
are  found    angular  nuclei.      From   the   intermediary 


122 


Elements  of  Histology.        [Chap.  xv. 


plexus  pass  off  isolated  or  small  groups  of  primitive 
fibrillar,  which  pursue  their  course  in  the  interstitial 


Fig. 


-Bundles  of    Non-striped    Muscular    Tissue    surrounded  by 
Plexuses  of  Fine  Nerve-fibres.    (Handbook.) 


Fig.  76a.— Termination  of  Nerves  in  Non- 
striped  Muscular  Tissue. 

a,  Non-medullatecl  fibre  of  the  intermediary  plexus  ; 
b,  fine  intermuscular  fibrils  ;  c,  nuclei  of  muscular 
cells.    (Atlas.) 


substairce  be- 
tween  the 
muscle  cells ; 
these  are  the 
intermuscular 
fibrils  (Fig.  76  a). 
According  to 
F  r  a  n  k  e  n  haiiser 
and  Arnold, 
they      give     off 


ner 


fi 


ending 


fibrils, 
in     the 


nucleus 

nucleolus). 

cording 


(or 

Ac- 

to 

Elischer,  the 
primitive  fibrils 
terminate  on  the 
surface  of  the 
nucleus  with  a 
minute  swelling. 


Chap,  xv.]      Peripheral  Nerve-endings. 


123 


In  many  localities  there  are  isolated  ganglion  cells 
in  connection  with  the  intermuscular  fibres. 

159.  The  nerves  of  blood-vessels  are  derived 
from  the  sympathetic,  and  they  terminate  in  arteries 
and  veins  in  essentially  the  same  way  as  in  non- 
striped  muscular  tissue,  being  chiefly  present  in  those 


% 


Fig.  77. — Plexus  of  Fine  Non-medullated  Nerve-fibres  surrounding 
Capillary  Arteries  in  the  Tongue  of  Frog,  after  staining  with 
Chloride  of  Gold. 

a,  Blood-vessel ;  6,  connective  tissue  corpuscles ;  c,  thick  non-niedullated  fibres ; 
d,  plexus  of  flue  nerve-fibres.    (Handbook.) 

parts  (media)  which  contain  the  non-striped  muscular 
tissue.  But  there  are  also  fine  non-medullated  nerve 
fibres,  which  accompany  capillary  vessels — capillary 
arteries  and  capillary  veins — and  in  some  places  they 
give  off  elementary  fibrils,  which  forma  network  around 
the  vessel  (Fig.  77).  In  some  localities  the  vascular 
nerve  branches  are  provided  with  small  groups  of 
ganglion  cells. 

160.  In  striped  muscle  of  man  and  mammals, 
reptiles,  and  insects,  the  termination  of  nerve  fibres 
takes  place,  according  to  the  commonly  accepted  view 
of  Kiihne,  in  the  following  manner  : — A  medullated 


124 


Elements  of  Histology. 


[Chap.  xv. 


nerve-fibre,  generally  derived  from  one  that  has 
divided,  enters  at  almost  a  right  angle  a  striped 
muscular  fibre,  the  neurilemma  becoming  fused  with 


Fig.  78. — From  a  Preparation  of  Striped  Muscular  Fibres  of  the  Snake, 
showing  the  termination  of  the  Medullated  Nerve-fibres.  (After 
a  preparation  of  Mr.  A.  Lingard.) 

a,  The  nerve  endplate  seen  from  the  broad  side ;  b,  the  same  seen  from  the 
narrow  side.  Each  endplate  is  a  network  connected  with  the  axis  cylinder 
of  a  medullated  nerve-fibre,  and  contains  numerous  nuclei  of  various  sizes 
and  shapes. 

the  sarcolemma,  and  the  nerve-fibre,  either  at  the 
point  of  entrance  or  soon  after  loses  its  medullary 
sheath,  so  that  only  the  axis  cylinder  passes  on. 
This  latter  divides  simultaneously  into  a  number  of 
smaller  fibres,  which  soon  break  up  into  a  network  of 
fine  fibrils,  this  ultimate  network  being  embedded  in  a 
more    or  less  granular-looking  plate,   provided   with 


Chap,  xv.]      Peripheral  Nerve-endings. 


125 


a  number  of  oblong  nuclei  (Fig.  78).  The  whole  struc- 
ture represents  the  nerve  endplate.  When  the  muscular 
fibre  contracts,  this  endplate  naturally  assumes  the 
shape  of  a  prominence — Doyere's  nerve-mount.  Each 
muscular  fibre  has  at  least  one  nerve  endplate,  but 
occasionally  has  several  in  near  proximity.  An 
endplate  is  generally  supplied  by  one,  sometimes, 
however,  by  two,  nerve-fibres.  The  contraction 
wave  generally  starts  from  the  endplate.  In 
Batrachia  the  nerve-fibre  does  not,  as  a  rule,  termi- 
nate in  the  shape  of  a  granular  endplate,  but 
having  penetrated  the  sarcolemma  ramifies  into 
several  axis  cylinders,  each  of  which  again  branches ; 
all  branches  have  a  more  or  less  longitudinal 
direction,  and  are  provided,  either  terminally  or   in 


Fig.  79. — Termination  of  Medullated  Nerve-fibres  in  Tendon,  near  the 
Insertion  of  the  Striped  Muscular  Fibres. 

The  nerve-flbres  terminate  in  peculiar  reticulated  endplates  of  primitive 
flbrillae.    (Golgi.) 

their  course,  with  oblong  nuclei.  Arndt  has 
shown  that  both  kinds  of  terminations  occur  in 
Batrachia.       These   two   sorts   of   nerve   endings  lie 


126 


Elements  of  Histology 


[Chap.  xv. 


underneath  the  sarcolemma  and  on  the  surface  of  the 
muscular  substance  proper.  But  besides  this  intra- 
muscular termination,  there  is  a  plexus  of  nerve-fibres, 
which  is  situated  outside  the  sarcolemma — i.e.,  inter- 
muscular;  this 
-    :     j  has  been  seen  by 

.^fSi^v^  Beale,     Kolliker, 

':^f^:-  Krause,        and 

others.  Arndt 

--— — - -^--i^i^TLL---- -  considers  these  in- 

:  -  jjp       ^--— — — Z!!^si"i  mii--a  termuscular  fibres 

---<->       =/     >  '        as  sensory  nerves. 

161.  Tendons 
-;  are  supplied  with 

4v  special  nerve  end- 

ings, studied  by 
Sachs,  Rollett, 
Gempt,  Rauber, 
and  particularly 
Golgi,  whose  work 
on  this  subject  is  very  minute.  These  terminations  are 
especially  numerous  near  the  muscular  insertion.    They 


Fig.  80. — One  of  the  Reticulated  Endplates 
of  the  previous  figure,  more  highly 
magnified. 

a,  The  medullated  nerve  fibre  ;  5,  the  reticulated 
endplate.    (Golgi.) 


Fig.  81.— Termination  of  Medullated  Nerve-fihres  in  Tendon. 

a,  End-bulbs  witb  convoluted  medullated  nerve-fibre;  6,  end-bulb  similar  to  a 
Herbst's  corpuscle.    (Golgi.) 

are  of  the  following  kinds  : — (a)  A  medullated  nerve 
fibre  branches  repeatedly,  and  the  axis  cylinder  breaks 
up  into  a  small  plate  composed  of  a  network  of  fine 
primitive  nerve-fibrils  (Fig.  79).     (b)  This  network  is 


chap,  xvi.]  The  Spinal  Cord.  127 

occasionally  embedded  in  a  granular-looking  material, 
and  thereby  a  similar  organ  as  the  nerve  endplate  of 
muscular  fibres  is  produced  (Fig.  80).  (c)  A  medul- 
lated  nerve-fibre  terminates  in  an  end-bulb  (Fig.  81), 
similar  to  those  of  the  conjunctiva,  or  of  a  Herbst's 
corpuscle. 


CHAPTER    XVI. 

THE    SPINAL    CORD. 

162.  The  spinal  cord  is  enveloped  in  three  distinct 
membranes.  The  outermost  one  is  the  dura  mater. 
This  is  composed  of  more  or  less  distinct  lamellae  of 
fibrous  connective  tissue  with  the  flattened  connective 
tissue  cells  and  networks  of  elastic  fibres.  The  outer 
and  inner  surface  of  the  dura  mater  is  covered  with 
a  layer  of  endothelial  plates. 

163.  Next  to  the  dura  mater  is  the  arachnoid 
membrane.  This  also  consists  of  bundles  of  fibrous 
connective  tissue.  The  outer  surface  is  smooth  and 
covered  with  an  endothelial  membrane  facing  the 
space  existing  between  it  and  the  inner  surface  of  the 
dura  mater  ;  this  space  is  the  sub-dural  lymph  space. 
The  inner  surface  of  the  arachnoidea  is  a  fenestrated 
membrane  of  trabecules  of  fibrous  connective  tissue, 
covered  on  its  free  surface — i.e.,  the  one  facing:  the 
sub-arachnoidal  lymph  space — with  an  endothelium. 

164.  The  innermost  membrane  is  the  pia  mater. 
Its  matrix  is  fibrous  connective  tissue,  and  it  is  lined 
on  both  surfaces  with  an  endothelial  membrane. 
Between  the  arachnoid  and  pia  mater  extends,  from 
the  fenestrated  portion  of  the  former,  a  spongy  plexus 
of  trabecular  of  fibrous  tissue,  the  surfaces  of  the 
trabecular  being  covered  with  endothelium.     By  this 


128  Elements  of  Histology.      [cup.  xvi. 

spongy  tissue — the  sub-arachnoidal  tissue  (Key  and 
Retzius) — the  sub-arachnoidal  space  is  subdivided  into 
a  labyrinth  of  lacunar  On  each  side  of  the  cord, 
between  the  anterior  and  posterior  nerve  roots, 
extends  a  spongy  fibrous  tissue,  called  ligamentum 
denticulatum,  between  the  arachnoidea  and  pia. 
By  it  the  sub-arachnoidal  space  is  subdivided  into 
an  anterior  and  posterior  division. 

165.  The  sub-dural  and  sub-arachnoidal  spaces  do 
not  communicate  with  one  another.  (Luschka,  Key 
and  Retzius.) 

The  dura  mater,  as  well  as  the  arachnoidea,  sends 
prolongations  on  to  the  nerve  roots;  and  the  sub- 
dural and  sub-arachnoidal  spaces  are  continued  into 
lymphatics  of  the  peripheral  nerves. 

All  three  membranes  contain  their  own  system  of 
blood-vessels  and  nerve-fibres. 

166.  The  cord  itself  (Fig.  82)  consists  of  an  outer 
or  cortical  part  composed  of  medullated  nerve-fibres ; 
this  is  the  white  matter,  and  an  inner  core  of  grey 
matter.  On  a  transverse  section  through  the  cord 
the  contrast  of  colour  between  the  white  mantle  and 
the  grey  core  is  very  conspicuous.  The  relation 
between  the  white  and  grey  matter  differs  in  diffe- 
rent parts ;  it  gradually  increases  in  favour  of  the 
former  as  we  ascend  from  the  lumbar  to  the  upper 
cervical  portion.  The  grey  matter  presents  in  every 
transverse  section  through  the  cord  more  or  less  the 
shape  of  a  capital  H;  the  projections  being  the 
anterior  and  posterior  horns  or  cornua  of  grey 
matter,  and  the  transverse  stroke  being  the  grey 
commissure.  In  the  centre  of  this  grey  commissure 
is  a  cylindrical  canal  lined  with  a  layer  of  columnar 
epithelial  cells ;  this  is  the  central  canal ;  the  part 
of  the  grey  commissure  in  front  of  this  canal  is 
the  anterior,  the  rest  the  posterior,  grey  commissure. 
The  shape  of  the  whole  figure  of   the   grey  matter 


Chap.  XVI.] 


The   Spinal    Cord. 


129 


differs  in  the  different  regions,  and  this  difference 
is  chiefly  brought  about  by  the  length  and  thickness 
of  the  grey  commissure.  In  a  section  through  the 
cervical  region  the  grey  commissure  is  thick  and 
short;  in  the  dorsal  region  it  becomes  thinner  and 


Fig.  82. — Transverse  Section  through  the  Spinal  Cord  of  Calf. 

a,  Pia  mater ;  5,  prolongation  of  pia  mater  into  the  anterior  longitudinal  fissure  ; 
c  posterior  longitudinal  fissure;  d,  anterior  column  of  white  matter  ;  e, 
lateral  column  of  same ;  /,  posterior  column  of  same ;  g,  anterior  white 
commissure ;  h,  central  canal ;  *,  anterior  horn  of  grey  matter  ;  j,  posterior 
horn  of  grey  matter ;  k,  anterior  nerve  roots ;  I,  posterior  nerve  roots. 


longer  ;  and  in  the  lumbar  region  it  is  comparatively 
very  thin  and  long.  Besides  this,  of  course  the  relative 
proportions  of  grey  and  white  matter,  as  mentioned 
before,  indicate  the  region  from  which  the  particular 
part  of  the  cord  has  been  obtained.  In  the  lower 
J 


130  Elements  of  Histology,       [Chap.  xvi. 

cervical  and  lumbar  region  where  the  nerves  of  the 
brachial  and  sacral  plexus  respectively  join  the  cord, 
this  latter  possesses  a  swelling,  and  the  grey  matter 
is  there  increased  in  amount,  the  swelling  being  in 
fact  due  to  an  accumulation  of  grey  matter,  in  which 
an  additional  number  of  nerve-fibres  originates ;  but 
the  general  shape  of  the  grey  matter  is  there  retained. 

167.  The  cornua  of  the  grey  matter  are  generally 
thicker  near  the  grey  commissure;  they  become  thinned 
out  into  anterior  and  posterior  edges  respectively, 
which  are  so  placed  that  they  point  towards  the 
antero-lateral  and  postero-lateral  fissures.  The  an- 
terior horns  are  generally  thicker  and  shorter  than 
the  posterior  ones,  and,  therefore,  the  latter  reach 
nearer  to  the  suface  than  the  former. 

168.  The  white  matter  is  composed  chiefly  of 
medullated  nerve  fibres  running  a  longitudinal  course. 
They  are  arranged  into  columns,  one  anterior,  one 
lateral,  and  one  posterior  column  for  each  lateral 
half  of  the  cord ;  the  two  halves  being  indicated  by 
the  anterior  and  posterior  median  longitudinal 
fissure.     The  anterior  median  fissure  is  a  real  fissure 

extending  in  a  vertical  direction  from  the  surface  of 
the  cord  to  near  the  anterior  grey  commissure.  It 
contains  a  prolongation  of  the  pia  mater  and  in  it 
large  vascular  trunks.  The  posterior  fissure  is  not 
in  reality  a  space,  but  is  filled  up  by  neuroglia.  It 
extends  as  a  continuous  mass  of  neuroglia  in  a  vertical 
direction  from  the  posterior  surface  of  the  cord  to  the 
posterior  grey  commissure.  The  exit  of  the  anterior 
or  motor  nerve  roots,  and  the  entrance  of  the  posterior 
or  sensitive  nerve  roots  are  indicated  by  the  anterior 
lateral  and  posterior  lateral  fissures  respectively. 
These  are  not  real  fissures  in  the  same  sense  as  the 
anterior  median  fissure,  but  correspond  more  to  the 
posterior  median  fissure,  being  in  reality  filled  up  with 
neuroglia   tissue,  into  which  extends  a  continuation 


Chap.  XVI.] 


The  Spinal  Cord. 


131 


from  the  pia  mater  with  large  vascular  trunks.  The 
white  matter  between  the  anterior  median  and  ante- 
rior lateral  fissure  is  the  anterior  column,  that  between 
the  anterior  lateral  and  posterior  lateral  fissure  is  the 
lateral  column,  and  that  between  the  posterior  lateral 
and  posterior  median  fissure  is  the  posterior  column. 
169.  Besides  the  septa  situated  in  the  two  lateral 


Fig.  83. — Diagram  of  a  Transverse  Section  through  the  Cord  in  the 
region  of  the  Cervical  Swe  ling. 

a,  Anterior  longitudinal  fissure  ;  6,  posterior  longitudinal  fissure :  the  part  of  the 
white  matter  next  to  it  is  the  fasciculus  of  Goll ;  c,  central  canal ;  rf,  direct 
pyramidal  fasciculus  ;  e,  roots  of  anterior  or  motor  nerves ;  /,  lateral  bundle 
of  posterior  nerve  roots;  g,  median  bundle  of  same;  ft,  the  cuneate  fasci- 
culus :  i,  the  crossed  pyramidal  fasciculus  or  the  fasciculus  of  Turk  ;  k,  the 
anterior  radicular  zone  of  the  lateral  column  of  white  matter ;  l,  the  direct 
cerebellar  fasciculus ;  m,  the  anterior  horn  of  grey  matter ;  «,  the  posterior 
horn  of  same. 


fissures  respectively,    there  are    other  smaller  septa, 
neuroglia  tissue  and  prolongations  of  the  pia  mater, 


132  Elements  of  Histology.       [Chap.  xvi. 

which  pass  in  a  vertical  and  radiating  direction  into 
the  white  matter  of  the  columns,  and  they  are  thus 
subdivided  into  a  number  of  smaller  portions ;  one 
such  bjg  septum  is  sometimes  found  corresponding  to 
the  middle  of  the  circumference  of  one  half  of  the 
cord.  This  is  the  median  lateral  fissure,  and  the 
lateral  column  is  subdivided  by  it  into  an  anterior 
and  posterior  division. 

Similarly,  the  anterior  and  posterior  columns 
may  be  subdivided  into  a  median  and  lateral  division 
(Fig.  83). 

170.  Some  of  these  various  subdivisions  bear 
definite  names  (Turk,  Charcot,  Mechsig)  : — 

(a)  The  median  division  of  the  anterior  column  is 
called  the  direct  or  uncrossed  pyramidal  fasciculus, 
being  a  continuation  of  that  part  of  the  anterior 
pyramidal  tract  of  the  medulla  oblongata  (see*  below) 
that  does  not  decussate. 

(b)  The  anterior  division  of  the  lateral  column  is 
called  the  anterior  radicular  zone. 

(c)  The  direct  cerebellar  fasciculus  corresponds  to 
the  peripheral  portion  of  the  postero-lateral  column  ; 
it  is  a  direct  continuation  of  the  white  matter  of  the 
cerebellum. 

(d)  The  posterior  division  of  the  lateral  column 
inside  the  cerebellar  fasciculus  is  called  the  fasciculus 
of  Turk,  or  the  crossed  portion  of  the  pyramidal  fasci- 
culus, it  being  a  continuation  of  the  decussated  part  of 
the  anterior  pyramidal  tract  of  the  medulla  oblongata. 

(e)  The  lateral  division  of  the  posterior  column, 
with  the  exception  of  a  small  peripheral  zone,  is  the 
cuneiform  or  cuneate  fasciculus,  or  posterior  radicular 
zone. 

(/)  The  median  division  of  the  posterior  column  is 
called  the  fasciculus  of  Goll. 

This  part  is  connected  directly  with  the  median 
bundle  of  the  posterior  nerve  roots.     {See  below.) 


Chap.  XVI.] 


The  Spinal  Cord. 


i33 


These  various  divisions  can  be  traced  from  the 
medullata  oblongata  into  the  cervical,  and  a  greater 
or  smaller  portion  of  the  dorsal  part  of  the  cord,  but 
farther  down  most  of  them  are  lost  as  separate  tracts, 
except  the  fasciculus  of  Turk. 

171.  The  ground  sud  stance  (Fig.  84)  of  both 
the  white  and  grey  matter — i.e.,  the  substance  in 
which    nerve-fibres, 

nerve  cells,  and  blood- 
vessels are  embedded — 
is  a  peculiar  kind  of  con- 
nective tissue,  which 
is  called  by  Yirchow 
neuroglia  and  by  Kol- 
liker  supporting  tissue. 
It  consists  of  three  dif- 
ferent kinds  of  ele- 
ments :  (a)  a  homoge- 
neous transparent  semi- 
fluid matrix,  which  in 
hardened  sections  ap- 
pears more  or  less  gran- 
ular; (b)  a  network  of 

very  delicate  fibrils — neuroglia  fibrils — which  are 
similar  in  some  respects,  but  not  quite  identical  with 
elastic  fibres. 

In  the  columns  of  the  white  matter  the  fibrils  extend 
pre-eminently  in  a  longitudinal  direction,  in  the  grey 
matter  they  extend  uniformly  in  all  directions,  and  in 
the  septa  between  the  columns  they  extend  chiefly  in 
the  direction  vertical  to  the  long  axis  of  the  cord. 

(c)  Small  branched  nucleated  cells  intimately 
woven  into  the  network  of  neuroglia  fibrils.  These 
cells  are  the  neuroglia  cells.  The  greater  the  amount 
of  neuroglia  in  a  particular  part  of  the  white  or  grey 
matter  the  more  numerous  are  these  three  elements. 

172.  In   both   the   white   and   grey   matter   the 


m£m^MS^^^ 


Fig.  84. — From  a  Transverse  Section 
through  a  most  Peripheral  Part  of 
the  White  Matter  of  the  Cord. 

c,  A  special  peripheral  condensation  of 

'  neuroglia;  w,  white  matter  with  the 

medullated     nerve-flhres     shown     in 

cross  section,  and  neuroglia  between 

them.    (Atlas.) 


134  Elements  of  Histology.       [Chap.  xvt. 

neuroglia  has  a  very  unequal  distribution ;  but  there 
are  certain  definite  places  in  which  there  is  always  a 
considerable  amount — a  condensation,  as  it  were,  of 
neuroglia  tissue.  These  places  are  :  underneath  the 
pia  mater — i.e.,  on  the  outer  surface  of  the  white 
matter — there  most  of  the  neuroglia  fibrils  have  a 
horizontal  direction  ;  near  the  grey  matter  there  is 
a  greater  amount  of  neuroglia  between  the  nerve- 
fibres  of  the  white  matter  than  in  the  middle  parts  of 
this  latter ;  in  the  septa  between  the  columns  and 
between  the  divisions  of  columns  of  white  matter  ;  at 
the  exit  of  the  anterior  and  the  entrance  of  the 
posterior  nerve  roots. 

A  considerable  accumulation  of  neuroglia  is 
present  immediately  around  the  epithelium  lining  the 
central  canal ;  this  mass  is  cylindrical,  and  is  called 
the  central  grey  nucleus  of  Kolliker.  The  epithelial 
cells  lining  the  central  canal  are  conical,  their  bases 
facing  the  canal,  their  pointed  extremity  being  drawn 
out  into  a  fine  filament  intimately  interwoven  with 
the  network  of  neuroglia  fibrils.  In  the  embryo  and 
young  state,  the  free  base  of  the  epithelial  cells  has  a 
bundle  of  cilia,  but  in  the  adult  they  are  lost. 

Another  considerable  accumulation  of  neuroglia 
exists  in  the  posterior  portion  of  the  posterior  grey 
horns,  as  the  substantia  gelatinosa  of  Rolando. 

173.  Ttie  white  matter  (Fig.  85)  is  composed, 
besides  neuroglia,  of  medullated  nerve-fibres  varying 
very  much  in  diameter,  and  forming  the  essential  and 
chief  part  of  it.  They  possess  an  axis  cylinder  and 
a  thick  medullary  sheath  more  or  less  laminated,  but 
are  devoid  of  a  neurilemma  and  its  nerve  corpuscles. 
Of  course,  no  nodes  of  Ranvier  are  observable.  In 
specimens  of  white  matter  of  the  posterior  columns, 
where  the  nerve-fibres  have  been  isolated  by  teasing 
or  otherwise,  many  fine  medullated  fibres  are  met 
with  which  show  the  varicose  appearance  mentioned 


Chap.  XVI.] 


The  Spinal   Cord. 


135 


Fig.  85.— From  a  Transverse  Section 
through  the  White  Matter  of  the  Cord. 

Showingthe  transversely-cut  medullated  nerve- 
fibres,  the  neuroglia  between  them  with  two 
branched  neuroglia  cells.  (Atlas.) 


in  a  former  chapter.  The  medullated  nerve-fibres, 
or  rather  the  matrix  of  their  medullary  sheath,  con- 
tains neurokeratin.  The  nerve-fibres  of  the  white 
matter  run  chiefly 
in  a  longitudinal 
direction,  and  they 
are  separated  from 
one  another  by  the 
neuroglia.  Here  and 
there  in  the  columns 
of  white  matter  are 
seen  connective  tis- 
sue septa  with  ves- 
sels, by  which  the 
nerve  -  fibres  are 
grouped  more  or 
less  distinctly  in 
divisions. 

174.  Although 
most  of  the  nerve-fibres  constituting  the  columns  of 
white  matter  are  of  a  longitudinal  direction — i.e., 
passing  upwards  or  downwards  between  the  grey 
matter  of  the  cord  on  the  one  hand,  and  the  brain  and 
medulla  oblongata  on  the  other — there  are  nevertheless 
a  good  many  nerve-fibres  and  grojips  of  nerve-fibres 
which  have  an  oblique  or  even  horizontal  course. 

(1)  The  anterior  median  fissure  does  not  reach 
the  anterior  grey  commissure,  for  between  its  bottom 
and  the  latter  there  is  the  white  commissure.  This 
consists  of  bundles  of  medullated  nerve-fibres  passing 
in  a  horizontal  or  slightly  oblique  manner  between  the 
grey  matter  of  the  anterior  horn  of  one  side,  and  the 
anterior  white  column  of  the  opposite  side  (Fig.  82,#). 

(2)  Numerous  medullated  fibres  are  derived  from 
the  grey  matter,  and  they  pass  in  a  horizontal  or 
oblique  direction  into  the  white  matter,  especially  in 
considerable  numbers  into  that  of  the  lateral  columns. 


136  Elements  of  Histology.       [Chap.  xvi. 

Having  entered  the  white  matter,  they  take  a  longitu- 
dinal direction.  Most  of  these  fibres  enter  the  white 
matter  in  the  septa  and  septula,  by  which  the  nerve- 
fibres  of  the  white  matter  of  the  columns  are  sub- 
divided, and  having  passed  in  a  horizontal  direction 
in  the  septa  and  septula,  some  for  a  shorter,  others 
for  a  longer  distance,  they  enter  the  columns  and 
pursue  a  longitudinal  course. 

175.  (3)  The  medullated  nerve-fibres  which  leave 
the  cord  by  the  anterior  nerve  roots  are  comparatively 
thick  fibres,  which  pass  out  of  the  anterior  portion  of 
the  grey  matter  of  the  anterior  horns  in  bundles ; 
they  pass  through  the  white  matter  in  an  oblique 
direction  by  septa,  and  emerge  in  the  anterior  lateral 
fissure  above  mentioned. 

(4)  The  medullated  nerve-fibres  entering  the  cord 
by  the  posterior  nerve  roots  are  thinner  than  those  of 
the  anterior  nerve  roots  ;  they  pass  into  the  cord  by 
the  posterior  lateral  fissure.  Having  entered,  they 
divide  into  two  bundles,  one  median  and  another 
lateral.  The  fibres  of  the  former  pass  in  an  oblique 
direction  into  the  white  matter  of  the  posterior 
columns — the  cuneiform  fasciculus  (see  above) ; — and, 
having  run  in  these  in  a  longitudinal  direction,  again 
leave  them,  sooner  or  later,  and  enter,  in  a  horizontal 
or  slightly  oblique  direction,  the  grey  matter  of  the 
posterior  horns.  The  fibres  of  the  lateral  bundle, 
on  the  other  hand,  pass  directly  from  the  posterior 
nerve  root  into  the  hindmost  portion  of  the  grey 
matter  of  the  posterior  horn.  The  nerve-fibres  of 
the  posterior  roots  entering  the  grey  matter  divide 
repeatedly,  and  show  very  markedly  the  varicose 
appearance. 

176.  The  grey  matter  consists,  besides  the 
uniform  network  of  neuroglia  fibres  and  neuroglia 
cells,  of  nerve-fibres  and  of  nerve-cells,  or  ganglion  cells. 

The   nerve-fibres  are  of  three  kinds — medullated 


Chap,  xvi.]  The  Spinal  Cord.  137 

fibres,  simple  axis  cylinders  of  various  sizes,  and  primi- 
tive nerve-fibrillse. 

The  medullated  nerve-fibres  run  a  more  or  less 
horizontal  course,  and  they  belong  to  different 
sources : — 

(1)  Medullated  nerve-fibres  connected  directly — 
i.e.,  by  the  axis  cylinder  process  (see  below) — with 
ganglion  cells  of  the  anterior  horns ;  they  leave  the 
anterior  horns  by  the  septa  and  septula,  and  they 
form  the  anterior  nerve  roots. 

(2)  Medullated  nerve-fibres  which  form  the  an- 
terior white  commissure ;  they  are  traceable  from  the 
anterior  column  of  one  side  into  the  grey  matter  of 
the  anterior  horns  of  the  opposite  side,  as  has  been 
mentioned  above;  some  of  these,  at  any  rate,  are 
distinctly  and  directly  traceable  to  ganglion  cells. 

(3)  Medullated  nerve-fibres  derived  indirectly 
from  the  median  bundle  of  the  posterior  nerve  root — 
i.e.,  coming  out  of  the  cuneiform  fasciculus  of  the 
posterior  column  and  medullated  nerve-fibres  derived 
directly  from  the  lateral  bundle  of  the  posterior  nerve- 
root.  Both  these  kinds  of  nerve-fibres  can  be  traced 
for  longer  or  shorter  distances  in  the  grey  matter  of 
the  posterior  horns ;  on  their  way  they  undergo 
numerous  divisions  into  very  fine  medullated  fibres. 

(4)  Medullated  nerve-fibres  passing  from,  the  grey 
matter  into  the  white  matter  of  the  lateral  column.  Some 
of  these  are  nerve-fibres  that  pass  simply  through  the 
grey  matter  of  the  anterior  horns  from  an  anterior 
nerve  root ;  others  are  derived-  directly  from  ganglion 
cells  forming  the  columns  of  Clarke  in  the  dorsal 
region  {see  below).  But  the  majority  are  derived  from 
that  part  of  the  grey  matter  intermediate  between  the 
anterior  and  posterior  horn. 

177.  The  simple  axis  cylinders  are  found  very 
numerously  in  the  grey  matter  of  all  parts ;  they  are 
of  many  various  sizes,  and  run  in  all  directions,  many 


138  Elements  of  Histology.       [Chap,  xvi. 

of  them,  especially  the  larger  ones,  are  only  the  first 
part  of  the  medullated  nerve-fibres,  being  the  axis 
cylinder  process  of  a  ganglion  cell,  which  process, 
after  a  shorter  or  longer  course  in  the  grey  matter, 
becomes  ensheathed  in  a  medullary  sheath,  and  re- 
presents one  of  the  above  medullated  fibres.  But 
there  are  also  numerous  fine  axis  cylinders,  which  are 
the  last  outrunners  of  the  nerve-fibres  entering  the 
grey  matter  by  the  posterior  roots.  They  are  seen 
everywhere,  isolated  and  running  in  smaller  or  larger 
bundles. 

178.  The  'primitive  nerve  fibrillce  form  the  greater 
part  of  the  grey  matter,  in  fact  the  matrix  of  the 
grey  matter  of  all  parts  being  composed,  besides  the 
network  of  neuroglia  fibrils,  of  an  exceedingly  fine 
and  dense  netivork  of  primitive  fibrillar  (Gerlach). 
These  are  the  nervous  groundwork  into  which  pass, 
and  from  which  originate,  nerve-fibres.  The  nerve- 
fibres  which  are  derived  from  the  posterior  roots 
having  entered  the  grey  matter  of  the  posterior 
horn  undergo  repeated  divisions,  and  ultimately  be- 
come connected  with  this  network  of  primitive 
fibrillse.  Numerous  nerve-fibres  take  their  origin  in 
the  network  of  primitive  fibrillse,  and  leave  the  grey 
matter  as  medullated  nerve-fibres,  which  pursue  a 
longitudinal  course  in  the  anterior  and  especially  in 
the  lateral  column  of  the  white  matter. 

179.  The  ganglion  cells  (Fig.  86)  of  the  grey 
matter  are  of  various  sizes  and  shapes,  the  branched,  or 
stellate,  or  multipolar  shape  being  predominant ;  some 
have  a  more  or  less  spindle-shaped  or  bipolar  body,  but 
each  extremity  may  be  richly  branched.  Each  has  a 
relatively  large  nucleus  bordered  by  a  membrane,  and 
in  it  is  a  reticulum  with  one  or  two  nucleoli.  The 
largest  ganglion  cells  occur  in  the  anterior  horns, 
likewise  in  the  Clarke's  column  of  the  dorsal  region  ; 
the  smallest  in  the  posterior  horns.    The  ganglion  cells 


Chap.  XVI.] 


The  Spinal  Cord. 


139 


are  much  more  numerous  in  the  anterior  horn  than  in 
the  posterior,  where  they  are  relatively  scarce. 

In  the  former  they  are  all  stellate  or  multipolar, 
and   form   definite   groups :    (a)    an   anterior   group, 


Fig.  86.— An  Isolated  Ganelion  Cell  of  the  Anterior  Horn  of  the 
Human  Cord. 

a,  Axis  cylinder  process  ;  5,  pigment.  The  branched  processes  of  the  ganglion 
cell  break  up  into  the  fine  nerve  network  shown  in  the  upper  part  of  the 
figure.    (Gerlach,  in  Strieker's  "  Manual  of  Histology.") 

(b)  a  median  or  inner  group,  and  (c)  a  lateral  group. 
The  cells  of  the  lateral  group  are  the  largest,  those  of 
the  inner  or  median  group  are  the  smallest  of  the 
three.  The  lateral  group  of  ganglion  cells  extends  in 
the  cervical  region  for  a  longer  or  shorter  distance 
into  the  white  matter  of  the  lateral  column. 


140 


Elements  of  Histology.       [Chap.  xvi. 


180.  In  the  dorsal  region  of  the  cord  there  exists 

near  the  grey  commissure 
a  special  cylindrical  group 
of  large  multipolar  gan- 
glion cells,  which  form  the 
column  of  Lockhart  Clarke. 

In  the  posterior  horns 
the  ganglion  cells  are  few 
and  far  between.  Most  of 
them  belong  to  the  portion 
of  the  posterior  horn  near 
the  posterior  commissure. 

The  substance  of  the 
ganglion  cells  is  fibrillated, 
but  there  exists  a  granular 
interstitial  material,  which 
is  especially  well  developed 
near  the  nucleus.  Some- 
times smaller  or  larger 
masses  of  yellowish  pig- 
ment granules  are  present 
in  this  part,  of  the  cell 
substance — i.e.,  near  the 
nucleus. 

181.  The  fibrillated  sub- 
stance of  the  ganglion  cells 
is  prolonged  on  to  the  pro- 
cesses. There  are  always 
one  or  two  that  are  thicker 
than  the  others.  At  a 
Fig.  87.-An  isolated  Multipolar   longer   or  shorter  distance 

Ganglion  Cell  of  the  Grey  Matter    from  the    Cell   the  JJTOCesses 

Th°e  L^riLi'iy-branchea  process  branch    dendritically    into 
ttJ^2^SE$g£ll   a  large  number  of   fibres' 

fibre  derived  from  a  posterior  nerve     wViir»h  AVAnrnnllv  brPflV    im 
root.    (Gerlach,  in  Strieker's  Manual.)    WHICH  eventually   OiedK.    up 

into   the   fine   network    of 
primitive  fibrillar,  forming  the  nervous  groundwork  of 


chap,  xvi.]  The  Spinal  Cord.  141 

the  grey  matter  (Fig.  87).  The  ganglion  cells  of  the 
anterior  horn  and  the  cells  of  Clarke's  column  have, 
in  addition  to  these  branched  processes,  generally  one 
unbranched  pale  process  (occasionally,  but  rarely,  this 
is  double),  which  takes  its  origin  in  the  cell  substance 
with  a  thin  neck.  This  is  the  axis  cylinder  process  of 
Deiters ;  it  becomes  invested  sooner  or  later  in  a 
medullary  sheath,  and  then  represents  a  medullated 
nerve-fibre,  as  mentioned  on  a  former  page.  The 
ganglion  cells  of  the  posterior  horns  have  no  axis 
cylinder  process,  all  processes  being  branched  and 
connected  with  the  ground  nerve  network  in  the  same 
way  as  the  branched  processes  of  the  ganglion  cells  of 
the  anterior  horns. 

Anastomoses  between  the  processes  of  the  ganglion 
cells  of  the  anterior  horns  have  been  observed  in  a 
few  instances  (Carriere). 

182.  The  ganglion  cells  of  the  anterior  horns  and 
those  forming  Clarke's  column — i.e.,  the  ganglion 
cells  with  axis  cylinder  process — are  considered  as 
motor,  the  others  as  sensory  ganglion  cells  ;  that  is  to 
say,  the  former  are  connected  with  a  motor  nerve-fibre, 
the  latter  with  a  sensory  fibre ;  but  it  would  be  quite 
incorrect  to  say  that  all  motor  fibres  are  connected 
with  the  former,  all  sensory  fibres  with  the  latter. 

183.  The  white  and  grey  matter  is  supplied  with  a 
large  number  of  blood-vessels,  the  capillaries  being 
more  abundant  and  forming  a  more  uniform  network 
in  the  grey  than  in  the  white  matter ;  in  the  latter, 
most  of  them  have  a  course  parallel  with  the  long 
axis.  The  blood-vessels  are  ensheathed  in  lymph 
spaces  (perivascular  spaces  of  His),  and  the  ganglion 
cells  are  each  surrounded  by  a  lymph  space  {peri- 
cellular space). 


142  [Chap.  XVII. 


CHAPTER   XVII. 

THE    MEDULLA    OBLONGATA. 

184.  As  the  cervical  portion  of  the  cord  passes 
into  the  medulla  oblongata,  its  parts  alter  position, 
arrangement,  and  name  in  the  following  manner  : — 

(a)  The  anterior  median  fissure  is  continued  as 
far  as  the  medulla  extends.  The  posterior  fissure  of 
the  cord  is  also  continued  on  the  medulla,  but  in  the 
upper  portion  is  lost,  owing  to  the  fact  that  the 
central  canal,  which  in  the  cord  is  situated  in  about 
the  middle,  shifts  in  the  medulla  towards  the  posterior 
surface,  and  soon  altogether  opens  into  the  fourth 
ventricle. 

1 85.  (b)  The  tracts  of  white  matter  bordering  the 
anterior  median  fissure  of  the  medulla,  and  separated 
from  the  other  tracts  by  a  distinct  fissure  on  the 
surface,  are  the  pyramidal  tracts.  As  was  mentioned 
on  a  former  page,  the  median  portion  of  the  anterior 
columns  of  white  matter  of  the  cord — i.e.,  the  un- 
crossed or  direct  anterior  fasciculus — is  a  direct  pro- 
longation of  the  pyramidal  tract,  and  can  be  followed 
in  this  upwards  into  the  pyramids — i.e.,  the  oblong 
prominences  in  the  upper  part  of  the  medulla  next 
to  the  anterior  median  fissure — and  from  there  to 
the  pons  Varolii  and  farther  into  the  crus  cerebri 
A  major  portion  of  the  pyramidal  tract  crosses  in 
the  lower  portion  of  the  medulla,  in  the  anterior 
median  fissure — this  forms  the  pyramidal  decussation 
(Fig.  88).  These  crossed  bundles  enter  the  postero- 
lateral column  of  the  cord,  that  part  of  it  which  has 
been  mentioned  above  as  the  fasciculus  of  Turk.  The 
crossed  portion  of   the  pyramidal  tract  passes   into 


Chap. xvii.]     The  Medulla  Oblongata. 


i43 


the  pyramids  and  farther  on  into  the  pons  Varolii  and 
cms  cerebri. 

186.   The  greater  portion  of  the  anterior  column 


'ifPB 


Fig.  88. — Transverse  Section  through  the  Medulla.  Oblongata  in  the 
Eegion  of  the  Pyramidal  Decussation. 

fpy,  Anterior  pyramidal  tract ;  cga,  lateral  nucleus  of  grey  matter ;  fa,  part  of 
anterior  column  not  decussating  ;  ng,  nucleus  gracilis ;  g,  gelatinous  nucleus 
of  posterior  horn  ;  11,  spinal  accessory  nerve.    (Henle.) 

of  white  matter  of  the  cord  is  situated  deeper  in  the 
medulla  than  the  pyramidal  tracts. 

(c)  The  lateral  column  of  white  matter  of  the 
cord  can  be  traced  into  the  medulla  as  the  lateral 
tract.  In  the  upper  part  of  the  medulla  it  becomes 
hidden  from  view  by  the  olivary  bodies  and  the 
transversely  arranged  white  tracts.     The  lateral  tract 


144  Elements  of  Histology.      [Chap.  xvn. 

of  the  medulla  comprises  all  parts  of  the  lateral 
column  of  the  cord  including  that  portion  which  was 
mentioned  as  the  anterior  radicular  zone  and  the  direct 
cerebellar  fasciculus,  but  not  that  posterior  division 
of  it  which  was  mentioned  previously  as  the  fasciculus 
of  Turk,  or  the  crossed  pyramidal  fasciculus. 

(d)  The  posterior  column  of  the  white  matter  of  the 
cord  is  continuous  with  the  same  column  of  the  medulla. 
That  portion  of  it  which  lies  next  to  the  posterior 
median  fissure,  and  which  is  called  in  the  cord  the 
fasciculus  of  Goll,  is  in  the  medulla  called  the  fasciculus 
(or  funiculus)  gracilis.  In  the  upper  part  of  the 
medulla,  as  the  central  canal  opens  into  the  fourth  ven- 
tricle, the  fasciculus  gracilis  turns  in  an  oblique  manner 
outside,  and  forms  the  lateral  boundary  of  the  ventricle. 

1 87.  (e)  The  lateral  part  of  the  posterior  column  of  the 
cord,  which  was  mentioned  as  the  fasciculus  cuneatus,  is 
prolonged  into  the  medulla  under  the  same  name.  But 
between  the  two — i.e.,  the  fasciculus  gracilis  and  fasci- 
culus cuneatus — there  exists  another  tract,  which  is 
called  by  Schwalbe  funiculus  of  Rolando.  In  the 
upper  part  of  the  medulla  the  fasciculus  cuneatus 
becomes  covered  by  transverse  bundles  of  medullated 
nerve-fibres;  these  pass  from  the  anterior  median 
fissure  across  the  surface  of  the  pyramids  and  olivary 
body  in  a  transverse  direction  towards  the  posterior 
fissure,  but  before  reaching  this  take  an  upward 
direction.  These  bundles  are  the  external  arcuate 
fibres.  In  the  upper  part  of  the  medulla  the  ex- 
ternal arcuate  fibres,  part  of  the  funiculus  cuneatus 
and  funiculus  of  Rolando,  as  well  as  the  direct  cere- 
bellar fasciculus  of  the  lateral  column,  all  join  to  form 
a  prominent  tract  of  white  matter — the  corpus  resti- 
forme — which  enters  the  white  matter  of  the  cerebellar 
hemisphere  on  the  same  side ;  this  is  the  pedunculus 
cerebelli  ad  medullam  oblongatam,  or  the  lower  cere- 
bellar peduncle. 


Chap. xvii.]    The  Medulla  Oblongata.  145 

188.  (f)  In  the  region  of  the  pyramidal  decussation 
— i.e.,  the  lower  part  of  the  medulla  immediately  fol- 
lowing the  cervical  portion  of  the  cord — the  grey 
matter  of  the  cord  is  changed  in  its  disposition  by 
the  fasciculus  of  Turk  or  the  crossed  pyramidal 
fasciculus  passing  en  masse  from  the  lateral  column 
of  white  matter  through  the  anterior  horns  of  the 
grey  matter.  Hereby  the  anterior  portion  of  the 
grey  matter  of  the  cord  is  shut  off  from  the  rest  of 
the  grey  matter,  and  is  found  lying  near  the  surface  of 
the  lateral  column  of  the  lower  portion  of  the  medulla 
as  the  lateral  nucleus  of  grey  matter  (Fig.  88).  The 
main  part  of  the  anterior  horn,  however,  is  repre- 
sented by  the  reticular  formation  of  grey  matter. 
This  contains  in  its  lateral  portion,  at  any  rate,  the 
same  large  multipolar  motor  ganglion  cells  with  axis 
cylinder  processes  of  Deiters  and  nervous  ground- 
network  as  the  anterior  horn  of  the  cord ;  but  in 
addition  there  are  the  numerous  bundles  of  medul- 
lated  nerve-fibres  passing  through  it  in  transverse, 
oblique,  and  longitudinal  directions.  Some  of  these 
fibres  belong  to  the  continuation  of  the  anterior 
columns  of  white  matter  of  the  cord,  others  join  the 
fasciculus  gracilis  and  cuneatus,  and  a  third  kind  pass 
out  from  the  middle  line  of  the  medulla. 

189.  (g)  The  grey  matter  of  the  posterior  horns  of 
the  cord  undergoes  a  change  of  disposition  when  passing 
into  the  medulla.  Its  hindmost  portion  is  gradually 
shifted  outwards  by  the  development  of  the  reticular 
formation  of  grey  matter,  and  in  about  the  middle  of 
the  medulla  it  is  found  lying  near  the  surface  of  the 
lateral  column  as  the  tubercle  of  Rolando.  The  rest 
of  the  posterior  horn  remains  at  first  collected  around 
the  central  canal ;  but  as  this  gradually  approaches 
the  posterior  fissure,  in  order  to  open  as  the  fourth 
ventricle  above,  the  grey  matter  gradualty  expands 
laterally  into  the  funiculus  gracilis  and  cuneatus  of 

K 


146 


Elements  of  Histology.      [Chap.  xvn. 


Fig.  89.— Transverse  Section  through  the  Medulla  Oblongata  in  the 
Eegion  of  the  Fourth  Ventricle. 

fpy,  Anterior  pyramidal  tract;  /r,  rcstiform  bodies;  np,  nucleus  of  pyramids; 
no,  olivary  nucleus;  nna,  accessory  olivary  nucleus;  nh,  nucleus  of  hypo- 
glossal nerve;  nv,  nucleus  of  vagus;  ntf,  nucleus  of  glosso-puaryngeus; 
r,  raphe;  9,  glossopharyngeal  nerve;  12,  hypoglossal  nerve;  y,  horizontal 
fibres.   (.Henle.) 


chap,  xvii.]     The  Medulla   Oblongata.  147 

the  white  matter,  and  forms  one  distinct  accumulation 
of  grey  matter  in  each  of  these  funiculi ;  they  are 
respectively  the  nucleus  gracilis  and  the  nucleus 
cuneatus.  The  former  is  the  grey  matter,  in  the 
axis  cylinder  process  of  whose  ganglion  cells  the  nerve- 
fibres  of  the  funiculus  gracilis  originate  ;  but  in  the 
latter  only  a  portion  of  the  nerve-fibres  of  the 
funiculus  cuneatus  take  their  origin ;  since  another 
part  of  it  joins  the  restiform  body,  and  with  this 
passes  into  the  cerebellum. 

190.  In  the  upper  part  of  the  medulla — i.e.,  in  the 
region  of  the  fourth  ventricle — the  grey  matter  forms  a 
continuous  mass,  the  floor  of  the  fourth  ventricle  (Fig. 
89).  In  this  region  there  is  a  distinct  median  septum, 
by  which  the  medulla  is  divided  into  two  halves ;  this 
is  the  raphe.  It  represents  a  thin  membrane  of  nerve 
substance  extending  from  the  anterior  longitudinal 
fissure  to  near  the  middle  line  of  the  floor  of  the  fourth 
ventricle.  This  membrane  consists  of  white  matter 
in  the  shape  of  bundles  of  medullated  nerve-fibres 
passing  longitudinally,  transversely,  and  obliquely ; 
and  of  small  masses  of  grey  matter  interspersed 
between  the  nerve-bundles,  and  especially  at  the  side 
of  the  raphe,  where  nerve-fibre  bundles  pass  out  of 
it.  The  grey  matter  contains  multipolar  ganglion 
cells. 

191.  In  a  transverse  section  through  the  upper 
part  of  the  medulla,  we  find  at  the  side  of  the 
pyramid,  and  a  little  behind  it,  but  covered  on  the 
outer  surface  by  white  matter — i.e.,  the  bundles  of 
nerve-fibres  constituting  the  fibrse  arcuatse  externae — 
a  plicated  lamina  of  grey  matter  which  constitutes  the 
olivary  nucleus,  or  nucleus  dentatus  of  the  olivary 
body.  It  extends  with  its  posterior  portion  into  the 
reticular  formation.  Continuous  with  the  olivary 
nucleus,  but  situated  nearer  the  raphe,  is  a  small 
lamina  of  similar  grey  matter ;   this  is  the  accessory 


148  Elements  of  Histology.      [Chap.  xvii. 

olivary  nucleus.  In  both  nuclei  are  found  numerous 
multipolar  ganglion  cells,  each  with  an  axis  cylinder 
process. 

192.  The  grey  matter  at  the  floor  of  the 
fourth  ventricle  is  that  from  which  the  nerve  roots 
of  the  cerebral  nerves  (facial  auditory,  glossopharyn- 
geal, pneumogastric,  accessory,  and  hypoglossal)  origi- 
nate. The  ganglion  cells  in  it  are  of  various  sizes, 
and  are  aggregated  into  groups  which  represent  the 
"nuclei" — i.e.,  the  origin  of  the  above  nerves.  The 
thin  layer  of  grey  matter  forming  the  floor  of  the 
ventricle,  in  the  strict  sense,  is  neuroglia  only,  a  con- 
tinuation of  the  central  grey  nucleus  of  the  cord. 

The  nerve  cells  in  the  hypoglossal  nucleus  are 
the  largest ;  they  are  as  large  as  the  large  cells 
of  the  anterior  horns  of  the  cord.  The  cells  of 
the  glossopharyngeal  nerves  are  considerably  smaller. 
The  motor  nerve-fibres  (e.g.,  those  of  the  hypoglossal 
and  pneumogastric)  originate,  as  the  axis  cylinder 
process  of  the  multipolar  ganglion  cells,  in  exactly 
the  same  manner  as  was  mentioned  in  the  cord, 
but  the  sensory  nerve- fibres  of  these  nerves  originate 
from  the  nerve  ground  network,  into  which  the 
processes  of  the  ganglion  cells  of  these  nuclei  break  up. 

193.  In  the  lower  part  of  the  medulla,  as  long  as 
there  is  still  a  closed  central  canal,  we  find  next  to 
this  the  last  outrunners  of  the  groups  of  ganglion 
cells  representing  the  nucleus  of  the  spinal  accessory 
and  hypoglossal. 

As  we  pass  upwards,  and  as  the  central  canal 
opens  as  the  fourth  ventricle,  the  groups  of  ganglion 
cells  below  the  floor  of  the  ventricle  are  so  arranged 
that  we  find  near  the  median  line  the  group  repre- 
senting the  hypoglossal  nucleus ;  then,  farther  out- 
wards, several  groups  representing  several  sub-divisions 
of  the  pneumogastric  nucleus ;  still  farther  upwards, 
but  more  in  the  anterior  part  of  the  medulla,  the  nucleus 


Chap,  xviii.]     Cerebrum  and  Cerebellum.  149 

of  the  glossopharyngeal  nerve ;  and,  lastly,  but  more 
outwards  and  upwards,  several  divisions  of  the  nucleus 
of  the  auditory  nerve.  The  nerve-fibres,  originating 
in  these  nuclei,  pass  in  bundles  through  the  substance 
of  the  medulla  oblongata,  so  as  to  appear  on  the 
antero-lateral  surface.  Of  course  these  nerves,  the 
nuclei  of  which  are  situated  nearer  to  the  middle  line — 
e.g.,  the  hypoglossal  and  spinal  accessory — have  to  pass 
through  the  reticular  formation,  whereas  those  whose 
nuclei  are  situated  more  laterally  pass  only  through 
the  lateral  part  of  the  medulla. 


CHAPTER   XVIII. 

THE  CEREBRUM  AND  CEREBELLUM. 

194.  The  structure  of  the  dura  mater,  arachnoidea, 
and  pia  mater  of  the  brain  is  similar  to  that  of  the 
same  membranes  of  the  cord. 

As  has  been  shown  by  Boehm,  Key  and  Retzius, 
and  others,  the  deeper  part  of  the  dura  contains  peculiar 
ampullated  dilatations  connected  with  the  capillary 
blood-vessels,  and  representing  in  fact  the  roots  of  the 
veins. 

The  glandulce  Pacchioni,  or  arachnoidal  villi  of 
Luschka,  are  composed  of  a  spongy  connective  tissue, 
prolonged  from  the  sub-arachnoidal  tissue  and  covered 
with  the  arachnoidal  membrane.  These  prolongations 
are  pear-shaped  or  spindle-shaped,  with  a  thin  stalk. 
They  are  pushed  through  holes  of  the  inner  part  of 
the  dura  mater  into  the  venous  sinuses  of  tins  latter, 
but  are  covered  with  endothelium.  Injection  matter 
passes  from  the  sub-arachnoidal  spaces  through  these 
stalks   into    the   villi.      The   spaces  of   their  spongy 


150  Elements  of  Histology.    [Chap,  xviii. 

substance  become  thereby  filled  and  enlarged,  and 
finally  the  injection  matter  enters  the  venous  sinus 
itself.  The  pia  cerebralis  is  very  rich  in  blood-vessels, 
like  that  of  the  cord,  which  pass  to  and  from  the 
brain  substance.  The  capillaries  of  the  pia  mater 
possess  an  outer  endothelial  sheath.  The  plexus 
choroideus  is  covered  with  a  layer  of  polyhedral 
epithelial  cells,  which  are  ciliated  in  the  embryo  and 
young. 

195.  As- was  mentioned  of  the  cord,  so  also  in  the 
brain  the  sub-dural  lymph  space  does  not  communicate 
with  the  sub-arachnoidal  spaces  or  with  the  ventri- 
cles (Luschka,  Key  and  Retzius).  Nor  is  there  a 
communication  between  the  sub-arachnoidal  space  and 
the  epicerebral  space — i.e.,  a  space  described  by  His  to 
exist  between  pia  mater  and  brain  surface,  but  doubted 
by  others.  The  relations  between  the  cerebral  nerves 
and  the  membranes  of  the  brain,  and  the  lymph- 
spaces  of  both,  are  the  same  as  those  described  of 
the  cord  and  the  spinal  nerves  on  a  previous  page. 

196.  The  pia  mater  passes  with  the  larger  blood- 
vessels into  the  brain  substance  by  the  sulci  of  the 
cerebrum   and    cerebellum. 

In  the  white  and  grey  matter  of  the  brain  we 
find  the  same  kind  of  supporting  tissue  that  we 
described  in  the  cord  as  neuroglia.  It  is  also  in 
the  brain  composed  of  a  homogeneous  matrix,  of  a 
network  of  neuroglia  fibrils,  and  of  branched,  flat- 
tened neuroglia  cells,  called  Deiters'  cells. 

In  the  white  matter  of  the  brain  the  neuroglia 
contains  between  the  bundles  of  the  nerve-fibres  rows 
of  small  nucleated  cells ;  these  form  special  accumula- 
tions in  the  bulbi  olfactorii,  and  in  the  cerebellum. 
Lymph  corpuscles  may  be  met  with  in  the  neuroglia, 
especially  around  the  blood-vessels  and  ganglion  cells. 

All  the  ventricles,  including  the  aqueductus  Sylvii, 
are  lined  with   a  layer  of  neuroglia,  being  a  direct 


Chap,  xviii.]   Cerebrum  and  Cerebellum.  151 

continuation  of  the  one  lining  the  fourth  ventricle, 
and  this  asfain  being  a  direct  continuation  of  the 
central  grey  nucleus  of  the  cord.  Like  the  central 
canal  of  the  cord,  also,  the  ventricles  are  lined  with  a 
layer  of  ciliated  columnar,  or  short  columnar  epithelial 
cells. 

197.  The  blood-vessels  form  a  denser  capillary 
network  in  the  grey  than  in  the  white  matter  ;  in  the 
latter  the  network  is  pre-eminently  of  a  longitudinal 
arrangement,  i.e.,  parallel  to  the  long  axis  of  the 
bundles  of  the  nerve-fibres.  In  the  grey  cortex  of 
the  hemispheres  of  the  cerebrum  and  cerebellum,  many 
of  the  capillary  blood-vessels  have  an  arrangement 
vertical  to  the  surface,  but  are  connected  with  one 
another  by  numerous  transverse  branches. 

The  blood-vessels  of  the  brain  are  situated  in 
spaces,  perivascular  lymph-spaces,  traversed  by  fibres 
passing  between  the  adventitia  of  the  vessels,  and 
the  neuroglia  forming  the  boundary  of  the  space. 
There  are  no  real  lymphatic  vessels  in  the  grey  or 
white  substance. 

198.  The  white  matter  consists  of  medullated 
nerve-fibres,  which  like  those  of  the  cord  possess  no 
neurilemma  or  nuclei  of  nerve  corpuscles,  and  no 
constrictions  of  Ranvier.  The  nerve-fibres  are  of 
very  various  sizes,  according  to  the  locality.  Divisions 
occur  very  often.  When  isolated  they  show  the 
varicosities  mentioned  in  the  cord. 

The  §rey  matter  consists,  like  that  of  the  cord 
and  medulla,  besides  the  neuroglia,  of  a  very  fine  net- 
work of  elementary  nerve-fibrils  (Rindfleisch,  G-erlach), 
into  which  pass,  on  the  one  hand,  nerve-fibres,  and, 
on  the  other,  the  branched  processes  of  ganglion  cells. 

With  regard  to  the  structure  of  the  ganglion  cells 
of  the  brain  and  medulla,  what  has  been  mentioned 
of  the  ganglion  cells  of  the  cord  holds  good  as  to 
them.       Like  the  former,  those  of  the  medulla  and 


152  Elements  of  Histology,    [chap,  xviii. 

brain  are  situated  in  lymph  spaces  or  the  pericellular 
spaces  (Obersteiner). 

199.  We  now  follow  the  above  description  of 
the  structure  of  the  medulla  with  that  of  the  cere- 
bellum and  pons  Varolii. 

I.  The  cerebellum  is  composed  of  laminae, 
folds,  or  convolutions,  composed  of  secondary  folds, 
each  of  which  consists  of  a  central  tract  of  white 
matter  covered  with  grey  matter.  The  tracts  of  white 
matter  of  neighbouring  convolutions  of  one  lobe  or 
division  join,  and  thus  form  the  principal  tracts  of 
white  matter. 

The  white  matter  of  the  cerebellar  hemisphere  is 
connected  (a)  with  the  medulla  oblongata  by  the 
corpus  restiforme,  this  forming  the  inferior  peduncle 
of  the  cerebellum ;  (6)  with  the  cerebrum  by  the 
pedunculus  cerebelli  ad  cerebrum,  this  forming  the 
superior  pedunculus ;  and  (c)  with  the  other  cerebellar 
hemisphere  by  the  commissure  passing  through  the 
pons  Yarolii ;  this  is  the  pedunculus  cerebelli  ad 
pontem,  or  the  middle  pedunculus. 

200.  On  a  vertical  section,  through  a  lamina  of  the 
cerebellum  (Fig.  90),  the  following  layers  are  seen  :  (a) 
the  pia  mater  covering  the  general  surface,  and  pene- 
trating with  the  larger  blood-vessels  into  the  peripheral 
substance  of  the  lamina  ;  (b)  a  thick  layer  of  cortical 
grey  matter ;  (c)  the  layer  of  Purkinje's  ganglion 
cells  ;  [d)  the  nuclear  layer,  and  (e)  the  central  white 
matter. 

201.  The  layer  of  ganglion  cells  of  Purkinje  is  the 
most  interesting  layer ;  it  consists  of  a  single  row  of 
large  multipolar  ganglion  cells,  each  with  a  large 
vesicular  nucleus.  Each  possesses  also  a  thin  axis 
cylinder  process,  directed  towards  the  depth,  the 
cell  sending  out  in  the  opposite  direction — i.e.,  towards 
the  surface — a  thick  process  which  soon  branches 
like  the  antlers  of  a  deer,  the  processes  being  all  very 


Fig.  90.— Prom  a  Vertical  Section  through,  the  Grey  Matter  of  the 

Cerebellum  of  the  Dog. 

pm,  Pia  mater ;  p,  the  ganglion  cells  of  Purkinje ;  g,  tbe  nuclear  layer  ;  /,  the 

layer  of  nerve-fibres  (white  matter).    (Atlas.) 


154  Elements  of  Histology.    [Chap.  xvm. 

long- branched  and  pursuing  a  vertical  course  towards 
the  surface ;  sooner  or  later  they  all  break  up  into  the 
fine  nerve-ground  network  of  the  grey  cortex.  The 
longest  processes  reach  near  to  the  surface.  The 
layer  (b)  above  mentioned — i.e.,  the  cortical  grey 
matter — is  in  reality  the  terminal  nerve  network  for 
the  branched  processes  of  the  ganglion  cells  of 
Purkinje.  Sankey  maintains  that  in  the  human  cere- 
bellum there  are  also  other  smaller  multipolar  gang- 
lion cells  connected  with  the  processes  of  the  cells  of 
Purkinje. 

202.  The  nuclear  layer  contains  a  large  number  of 
spherical  or  slightly  oval  relatively  small  nuclei  em- 
bedded in  a  network  of  fine  fibrils,  the  nature  of 
which  is  not  definitely  ascertained — i.e.,  whether  it 
consists  of  neuroglia  only,  or  whether  it  contains, 
in  addition,  also  a  network  of  nerve  fibrils.  The  latter 
is  exceedingly  probable.  The  nuclei  are  nuclei  of 
neuroglia  cells,  of  lymph  corpuscles  and  of  small  gang- 
lion cells. 

The  axis  cylinder  process  of  the  ganglion  cell  of 
Purkinje  passes  through  the  nuclear  layer,  and  be- 
coming invested  with  a  medullary  sheath,  enters  as 
a  medullated  nerve-fibre  the  central  white  matter. 
There  are,  however,  medullated  nerve- fibres  of  the 
central  white  matter,  which  are  not  connected  with  an 
axis  cylinder  process  of  a  Purkinje's  cell,  but  enter 
the  nuclear  layer  and  probably  terminate  there  in  the 
nerve  network,  or  pass  through  it  and  terminate  in  the 
nerve  network  of  the  grey  matter  of  the  cortex. 

203.  II.  The  pons  Varolii  (Fig.  91)  is  a  pro- 
longation partly  of  the  medulla  and  partly  of  the 
cerebellum.  Of  the  latter  only  white  matter  passes 
transversely  into  the  anterior  portion  of  the  pons, 
and  forms  there  the  transverse  bundles  of  nerve-fibres, 
which  give  to  the  pons  the  horizontal  striation. 

As  we  pass  upwards — i.e.,  farther  away  from  the 


Chap,  xviii.]   Cerebrum  and  Cerebellum. 


i55 


medulla,  this  part  of  the  pons — i.e.,  that  composed  of 
horizontal  fibres — increases  in  thickness. 

204.  Of   the  medulla   there  is  a  greater   portion 


/  trs 


Fig.  91. — Transverse  Section  through  the  Lower  Corpus  Quadrigeminum 
and  the  Pons  Varolii. 

a,  Aqueductus  sylvii ;  b,  crossing  of  the  bracbia  of  tbe  lower  corp.  quadrig. ;  q, 
ganglion  of  tbe  lower  corp.  quadrig.;  s,pedunculus  of  the  lower  corp.  quadrig.; 
ba,  tegmentum  ;  5,  the  descending  root  of  the  fifth  ;  p,  bundles  of  tbe 
anterior  pyramidal  tracts  in  cross  section ;  trp,  deep  transverse  bundles 
of  tbe  pons ;  trs,  superficial  transverse  bundles  of  tbe  pons.  (Meynert,  in 
Strieker's  Manual.) 


continued  into  the  pons  than  of  the  cerebellum. 
(1)  There  are  the  pyramidal  tracts  ;  they  do  not  lie  on 
the  surface  as  in  the  medulla^  but  are  hidden  by  some 


156  Elements  of  Histology.    [Chap,  xviii. 

— the  most  anterior  bundles — of  the  transverse  fibres. 
The  bundles  of  the  pyramidal  tract  pass  as  longitudinal 
fibres  merely  through  the  anterior  half  of  the  pons, 
and  enter  the  crura  cerebri  where  they  form  the 
crusta.  (2)  The  raphe.  (3)  The  reticular  formation ; 
but  this  is  limited  to  the  posterior  part.  Small  masses 
of  grey  matter  and  ganglion  cells  are  scattered  every- 
where between  the  transverse  bundles  of  the  nerve- 
fibres  of  this  formation.  (4)  The  grey  matter  at  the 
floor  of  the  fourth  ventricle.  This  grey  matter  con- 
tains also  on  the  posterior  surface  of  the  pons  groups 
of  multipolar  ganglion  cells. 

Near  the  middle  line  there  is  a  group  of  large 
multipolar  ganglion  cells,  each  with  an  axis  cylinder 
process.  This  is  the  nucleus  for  the  sixth  nerve,  and 
of  part  of  the  seventh,  the  former  lying  more  median 
than  the  latter.  There  is  another  nucleus  of  the 
seventh  situated  more  deeply — i.e.,  in  the  reticular 
formation.  More  outwards  we  meet  with  the  superior 
nucleus  of  one  of  the  roots  of  the  auditory  nerve. 
Farther  upwards  we  meet  with  the  nucleus  of  the 
motor  roots  of  the  fifth. 

(5)  In  the  lower  part  of  the  pons  there  exists  also 
a  continuation  of  the  grey  matter  of  the  corpus  den- 
tatum  of  the  olivary  body. 

205.  The  pons  is  connected  with  the  cerebrum  by 
the  crusta  of  the  crus  cerebri,  which,  as  mentioned 
above,  are  bundles  of  medullated  nerve-fibres  passing 
merely  through  the  pons  but  being  continuations  of 
the  anterior  pyramidal  tracts  of  the  medulla. 

206.  III.  The  hemispheres  of  the  cere- 
brum.— On  a  vertical  section  each  convolution  shows 
a  white  centre  and  a  grey  cortex.  The  former  is  com- 
posed of  medullated  nerve-fibres.  The  white  matter 
of  the  convolutions  of  the  cerebral  hemispheres  is  ar- 
ranged as  (a)  the  centrum  ovale — i.e.,  the  central  mass 
of  white  matter  from  which  the  lamina  of  white  matter 


Chap,  xviii.]   Cerebrum  and  Cerebellum. 


*57 


for  each  convolution 
branches  off,  and,  (b), 
the  commissure  of  white 
matter  between  the  two 
hemispheres,  i.e.,  the 
corpus  callosum  and 
anterior  commissure. 
The  centrum  ovale  again 
consists  of  tracts  of 
medullated  nerve-fibre, 
which  connect  (a)  the 
convolutions  of  the  same 
hemisphere  with  one 
another,  and  (b)  such  as 
pass  between  the  con- 
volutions on  the  one 
hand,  and  the  thalamus 
opticus,  the  pons,  and 
medulla  on  the  other. 
These  tracts  pass  by  the 
internal  capsule  (see 
below)  to  the  thalamus 
opticus,  and  to  the  cms 
cerebri. 

The  grey  cortex  con- 
sists, according  to  Mey- 
nert,  of  the  following 
layers  (Fig.  92)  :— (1)  a 
superficial  layer  of  grey 


Fig.  92.  —  Vertical  Section 
through  the  Grey  Matter  of  a 
Cerebral  Convolution. 

a,  Superficial  layer ;  6,  closely- 
packed  small  ganglion  cells  ;  c,  the 

.  layer  of  the  cornu  Ammonis,  this 
being  the  principal  layer;  d,  the 
"  granular  formation,"  small 
multipolar  ganglion  cells;  e,  the 
layer  of  spindle-shaped  ganglion 
cells.  (Meynert,  in  Strieker's 
Manual.) 


i58 


Elements  of  Histology.    [Chap.  xvm. 


matter  (neuroglia  and  nerve  ground  network),  with 

few  and  small  ganglion  cells. 
(2)  A  layer  of  small  more  or 
less  pyramidal  ganglion  cells 
densely  aggregated.  (3)  The 
formation  of  the  cornu  Am- 
monis.  This  is  the  principal 
or  broadest  stratum  of  the 
cortex ;  it  is  composed  of 
several  layers  of  large,  pyra- 
midal ganglion  cells,  increas- 
ing in  size  as  a  deeper  layer 
is  reached. 

The   pyramidal   cells  of 
this  third  and  of  the  previous 
second  stratum  consist  of  a 
pyramidal  body  including  an 
oval  vesicular  nucleus  (Fig. 
93).   From  the  body  pass  out 
the  following  principal  pro- 
cesses : — (a)  the  process  of  the 
apex,   directed  towards  the 
surface  of  the  convolution ; 
it  can  be  traced  for 
a  longer   or    shorter 
distance.        (b)    The 
lateral     basilar    pro- 
cesses,     and     finally 
the     median    basilar 
process.     This  latter 
is   fine,   remains   un- 
branched,  and  is  an 

Fig.  93. -A  large  Pyramidal    Ganglion  axis  cylinder  process, 

Cell  of  the  Grey  Cortex  of  the  Human  £  q  becomilio-       in- 

Cerehrurn.  *'  .  * 

The  process  of  the  apex  and  the  other  processes  Vested.  Wltll  a  medul- 

branch  and  break  up  into  the  fine  nerve  net-  law  ulioaf  li  ica  norvo 

work.   The  median  process  of  the  base  of  the  lcl1  J  &llt5cluu  iS>  <*  uei  Vfc-~ 

pyramid  remains  un branched,  and  becomes  •£>»>»/%     r»f    fl-io     nontrnl 

an  axis  cylinder  of  a  nerve-flbre.    (Atlas.)  U.VLV     Ol     tat;     ceiiWeti 


chap,  xviii.]     Cerebrum  anl  Cerebellum.  159 

white  matter.  The  other  processes,  sooner  or  later  in 
their  course,  branch  and  break  up  finally  into  the 
nerve  ground  network  of  the  grey  matter.  (4)  A  thin 
stratum  of  small  irregular  branched  ganglion  cells,  the 
granular  formation  of  Meynert.  (5)  A  last  stratum 
of  spindle-shaped  and  branched  ganglion  cells,  ex- 
tending parallel  to  the  surface. 

207.  According  to  Meynert,  the  grey  cortex  of  the 
posterior  portion  of  the  occipital  lobe  about  the  sulcus 
hippocampi  consists  of  eight  layers,  the  granular  for- 
mation being  the  principal  one.  In  the  grey  cortex  of 
the  cornu  Ammonis,  on  the  other  hand,  the  third 
layer  is  the  principal  layer,  the  fourth  being  wanting. 
In  the  claustrum  (part  of  the  wall  of  the  fossa  Sylvii), 
the  spindle-shaped  cells  of  the  fourth  layer  form  the 
principal  stratum. 

208.  The  bulbus  olfactorius  contains  in  most 
mammals,  but  not  in  man,  a  small  central  cavity 
lined  with  columnar  ciliated  epithelial  cells.  The  sub- 
stance of  the  bulb  around  this  cavity  consists  of  an 
upper  part,  which  is  white  matter,  and  is  a  continua- 
tion of  the  tractus  olfactorius.  The  lower  part  is 
grey  matter,  and  contains  the  following  layers,  count- 
ing from  below  upwards  :  (1)  a  layer  of  non-medul- 
lated  nerve-fibres,  each  with  a  neurilemma ;  this  layer 
forms  farther  on  the  olfactory  nerve  going  to  the 
olfactory  organ  ;  (2)  the  stratum  glomerulosum,  com- 
posed of  a  number  of  glomeruli  or  convolutions, 
each  of  which  consists  of  an  olfactory  nerve-fibre,  and 
in  addition  to  it  numerous  small  neuroglia  cells  ;  (3) 
stratum  gelatinosum  of  Lockhart  Clarke,  composed 
of  a  fine  nerve  network,  and  embedded  in  it  multi- 
polar ganglion  cells ;  (4)  a  last  and  thickest  layer  of 
nuclei  embedded  in  a  network  of  fibrils,  and  similar  in 
structure  with  the  "  nuclear  layer." 

209.  IY.  The  mesencephalon. — The  fourth 
ventricle  above  the  upp-er  part  of   the  pons  Varolii 


160  Elements  of  Histology.    [ciaP.  xviii. 

closes  again  into  a  small  canal — the  aqueductus 
Sylvii — which  having  passed  in  front  out  of  the  region 
of  the  corpora  quadrigemina  opens  out  again  as  the 
third  ventricle.  The  parts  around  the  aqueductus 
Sylvii  represent  the  mesencephalon  (Fig.  91),  developed 
from  the  middle  brain  vesicle  in  the  embryo.  They 
include  the  wall  of  the  aqueductus  Sylvii,  the  corpora 
quadrigemina,  and  the  crura  cerebri. 

The  aqueductus  Sylvii  is  lined  with  epithelium 
and  a  layer  of  neuroglia  continued  from  the  fourth 
ventricle.  The  raphe  of  the  medulla  and  of  the  pons 
are  continued  into  the  lower  wall  of  the  aqueductus. 
The  lining  layer  of  neuroglia  is  on  its  frontal  aspect 
surrounded  by  a  layer  of  grey  substance  continued 
from  the  grey  substance  of  the  floor  of  the  fourth 
ventricle.  It  contains  in  a  nerve  network  numerous 
multipolar  ganglion  cells  grouped  into  nerve  nuclei, 
connected  with  the  third,  fourth,  and  part  of  the  fifth 
pair  of  nerves.  In  front  of  this  layer  is  one  of  con- 
siderable thickness  representing  the  tegmentum,  which 
is  the  dorsal  or  posterior  portion  of  the  crus  cerebri. 

210.  The  corpora,  quadrigemina. — Each  of 
the  two  inferior  prominences  consists  of  a  superficial 
layer  of  white  matter,  and  a  deep  grey  portion,  con- 
taining multipolar  ganglion  cells  of  various  sizes 
embedded  in  a  fine  nerve  network.  Between  this  and 
the  grey  substance  of  the  wall  of  the  aqueductus  Sylvii 
are  tracts  of  white  matter,  forming  part  of  the  Jillet. 
In  each  of  the  two  superior  prominences  there  is  also 
a  superficial  layer  of  white  matter,  beneath  which 
is  a  layer  of  grey  matter  (stratum  cinereum)  ;  under- 
neath this  is  the  main  portion — the  stratum  opticum — 
consisting  of  longitudinal  tracts  of  nerve-fibres,  be- 
tween which  are  small  masses  of  grey  substance. 
Between  this  stratum  opticum  and  the  grey  matter 
forming  the  wall  of  the  aqueductus  Sylvii  is  a  layer 
of  white  matter,  part  of  the  Jillet. 


Chap,  xviii.]   Cerebrum  and  Cerebellum.  161 

211.  The  crus  cerebri  of  each  side  consists  of  an 
anterior,  middle,  and  posterior  portion.  The  anterior 
or  ventral  portion  is  the  crusta,  or  pes ;  the 
posterior  or  dorsal  portion  is  the  tegmentum.  Be- 
tween the  two  is  the  substantia  nigra.  The  crusta  is 
composed  of  longitudinal  tracts  of  medullated  nerve- 
fibres  passing  from  the  margin  of  the  pons  Varolii 
to  the  internal  capsule  of  the  thalamencephalon,  and 
farther  into  the  white  matter  of  the  hemisphere. 

212.  The  tegmentum  has  been  mentioned  above 
as  being  situated  in  front  of  the  grey  matter  forming 
the  anterior  wall  of  the  aqueductus  Sylvii.  The 
tegmentum  is  a  prolongation  of  the  reticular  formation 
of  the  pons  Yarolii  and  medulla  (see  above),  i.e.,  small 
masses  of  grey  substance  separated  by  tracts  of  nerve- 
fibres,  most  of  which  run  in  a  longitudinal  or  transverse 
direction.  The  longitudinal  bundles  include  a  con- 
tinuation of  the  white  matter  of  the  cerebellum, 
mentioned  in  a  previous  page  as  the  superior 
peduncle  of  the  cerebellum,  or  the  pedunculus  cere- 
belli  ad  cerebrum.  These  undergo  total  decussation  in 
the  upper  part  of  the  mesencephalon,  and  ultimately 
enter  the  thalamus  opticus. 

213.  The  substantia  nigra  is  grey  matter 
situated  between  the  two  above ;  it  has  received  its 
name  from  the  numerous  dark  pigment  granules 
lodged  in  the  substance  of  its  ganglion  cells.  These 
are  small  and  multipolar. 

214.  V.  The  thalamencephalon  and  corpus 
striatum. — The  former  comprises  the  parts  of  the 
brain  situated  round  the  third  ventricle,  the  most  im- 
portant being  the  thalamus  opticus,  the  pineal  gland, 
the  corpora  albicantia,  the  infundibulum  and  tuber 
cinereum,  and  the  hypophysis  cerebri.  The  corpus 
striatum  is  the  ganglion  of  the  cerebral  hemisphere, 
with  which  it  originates  from  the  same  part — i.e.,  the 
frontal  part  of  the  first  cerebral  vesicle  of  the  embryo. 

L 


1 62  Elements  of  Histology.    [Chap,  xviii. 

215.  The  thalamus  opticus  consists  of  a  super- 
ficial layer  of  white,  and  a  centre  of  grey  matter. 
In  this  numerous  multipolar  ganglion  cells  are  noticed. 
The  white  matter  in  the  outer  portion  is  very  con- 
siderable, and  of  great  importance  from  its  connec- 
tions. From  it  radiate  tracts  of  medullated  nerve- 
fibres,  which  join  the  tracts  of  the  internal  capsule  on 
their  way  to  and  from  the  different  parts  of  the 
cerebral  hemisphere. 

The  superior  pedunculus  cerebelli,  after  its 
decussation  with  that  of  the  opposite  side,  passes 
into  the  white  matter  of  the  thalamus.  The  trac- 
tus  opticus  is  connected  with  the  outer  white  matter 
of  the  posterior  portion  of  the  thalamus — i.e.,  the 
pulvinar. 

216.  The  corpus  striatum,  as  stated  before, 
is  considered  as  the  ganglion  of  the  cerebral  hemi- 
sphere. It  consists  of  the  nucleus  caudatus  and  the 
nucleus  lenticularis.  The  former  projects  into  the 
lateral  ventricle,  the  latter  is  the  outer  portion  of 
the  corpus  striatum.  The  nucleus  lenticularis  is 
separated  from  the  nucleus  caudatus  and  from  the 
anterior  portion  of  the  thalamus  opticus  by  tracts  of 
medullated  nerve-fibres,  known  as  the  internal  capsule. 
On  the  outer  surface  of  the  nucleus  lenticularis  is  a 
thin  lamina  of  white  matter  which  is  the  external 
capsule.  This  is  separated  from  the  white  matter 
of  the  cerebral  convolutions  at  this  part — i.e.,  the 
island  of  Beil — by  a  thin  lamina  of  grey  matter,  called 
the  claustrum.  The  nucleus  caudatus  and  lenti- 
cularis consist  of  grey  matter  with  larger  and  smaller 
groups  of  multipolar  ganglion  cells,  permeated  by 
tracts  of  medullated  nerve-fibres,  which  originate  in 
the  grey  matter.  These  tracts  of  white  matter  pass 
transversely  and  obliquely  into  the  internal  capsule, 
and  are  to  be  traced  on  the  one  hand  to  the  white 
matter  of  the  convolutions  of  the  cerebral  hemisphere, 


chap,  xix.]   The  Cerebrospinal  Ganglia.         163 

which  is,  however,  doubted  by  many  observers,  and 
on  the  other  into  the  crusta  of  the  cms  cerebri. 

217.  The  internal  capsule  is  one  of  the  most 
important  masses  of  white  matter ;  it  contains  the 
tracts  of  medullated  nerve-fibres  which  pass  between 
the  white  matter  of  the  cerebral  hemisphere  and  the 
eras  cerebri — i.e.,  the  corona  radiata  of  Reil ;  further, 
it  contains  tracts  of  medullated  nerve-fibres  passing 
between  the  thalamus  opticus  and  the  white  matter 
of  the  cerebral  hemispheres ;  and,  finally,  it  contains 
tracts  of  nerve-fibres  passing  between  the  corpus 
striatum  and  the  crus  cerebri. 

218.  The  pineal  gland,  or  conarium,  and  the 
anterior  lobe  of  the  hypophisis  cerebri,  are  epithelial 
in  structure  and  origin,  and  will  be  described  in  a 
future  chapter.  The  pineal  gland  contains  a  large 
amount  of  calcareous  matter — brainsand. 

The  corpora  albicantia  are  masses  of  white 
matter  —  i.e.,  medullated  nerve-fibres;  each  corpus 
albicans  includes  a  centre  of  grey  substance. 

The  infundibulnm  and  tuber  cinereum  at  the  floor 
of  the  third  ventricle  are  composed  of  grey  matter  ; 
the  latter  extends  between  the  corpora  albicantia 
to  the  optic  commissure,  while  the  former  is  connected 
with  the  posterior  or  minor  lobe  of  the  hypophisis. 


CHAPTER   XIX. 

THE    CEREBRO-SPINAL    GANGLIA. 

219.  The  ganglia  connected  with  the  posterior 
roots  of  the  spinal  nerves,  and  with  some  of  the 
roots  of  the  cerebral  nerves — e.g.,  Gasserian,  otic, 
geniculate,  ciliary,  Meckel's  ganglion,  the  ganglia  of 


164 


Elements  of  Histology.      [Chap.  xix. 


the  branches  of  the  acoustic  nerve,  the  submaxillary 
ganglion,  &c. — possess  a  capsule  of  fibrous  connective 
tissue  continuous  with  the  epineurium  of  the  afferent 
and  efferent  nerve  trunks.  The  interior  of  the  ganglion 
is  subdivided  into  smaller  or  larger  divisions,  contain- 
ing nerve  bundles  with  their  perineurium,   or  larger 

and  smaller  groups  of  ganglion 
cells.  In  the  spinal  ganglia 
these  latter  are  generally  dis- 
posed about  the  cortical  part, 
whereas  the  centre  of  the 
ganglia  is  chiefly  occupied  by 
bundles  of  nerve-fibres. 

220.  The  ganglion  cells  differ 
very  greatly  in  size,  some  being 
as  big,  and  bigger,  than  a  large 
multipolar  ganglion  cell  of  the 
anterior  horn  of  the  cord,  others 
much  smaller.  Each  cell  has 
a  large  oval  nucleus,  including 
a  network,  with  one  or  two 
large  nucleoli.  Its  substance 
shows  a  distinct  fibrillation. 
Each  cell  of  the  ganglia  in  man 
and  mammals  is  unipolar  (Fig. 
94),  flask  or  pear-shaped,  and 
invested  in  a  hyaline  capsule, 
lined  with  a  more  or  less  con- 
tinuous layer  of  nucleated  endo- 
thelial cell-plates.  The  single 
process  of  the  ganglion  cell  is 
finely  and  longitudinally  stri- 
ated, and  is  an  axis  cylinder 
process.  Immediately  after 
leaving  the  cell  body  it  is  much 
convoluted  (Retzius) ;  then  it  gets  invested  in  a 
medullary  sheath — i.e.,  it  becomes  a  medullated  nerve- 


Fitf.  94.-A  large  and  small 
Ganglion  Cell  of  the  Gang- 
lion Gasseri  of  the  Rabbit. 

The  axis  cylinder,  after  leaving 
the  cell,  becomes  convoluted 
and  transformed  into  a  medul- 
lated nerve-fibre,  which  divides 
into  two  medullated  fibres. 
IKey  and  Retzius.) 


Chap,  xix.]   The  Cerebrospinal  Ganglia. 


165 


fibre.  The  capsule  of  the  ganglion  cell  is  continued 
on  the  axis  cylinder  process,  and,  farther  on,  on  the 
medullated  nerve-fibre,  as  the  neurilemma ;  while  the 
endothelial  plates  of  the  capsule  pass  into  the  nerve 
corpuscles  lining  the  neurilemma,  their 
number  greatly  diminishing  (Fig.  95). 

221.  In  the  rabbit  this  medullated 
nerve-fibre  at  its  first  node  of  Ranvier, 
which  is  not  at  a  great  distance  from 
the  ganglion  cell,  divides  into  two  me- 
dullated nerve-fibres  in  the  shape  of  a 
T ;  one  branch  is  supposed  by  Ranvier 
to  pass  to  the  cord,  the  other  to  the 
periphery.  In  man,  this  T-shaped 
division  has  also  been  observed  by 
Retzius,  but  it  cannot  be  said  with 
certainty  that  in  rabbit  or  man 
every  axis  cylinder  process  shows  this 
T-shaped  division.  Retzius  observed 
this  T-shaped  division  also  in  the 
Gasserian,  geniculate,  and  vagus  gan- 
glia in  man. 

The  ganglion  cells  are  not  unipolar 
in  all  cerebral  ganglia  ;  in  the  ciliary 
and  otic  ganglia  there  are  a  good  many 
ganglion  cells  which  are  multipolar. 

222.  Numerous  ganglia  of  micro- 
scopic sizes  are  to  be  found  in  the 
sub-maxillary  (salivary)  gland ;  they 
are  of  different  sizes,  and  are  in 
reality  ganglionic  enlargements  of 
larger  or  smaller  nerve-bundles.  Each 
ganglion  is  invested  in  connective 
tissue  continuous  with  the  perineu- 
rium, and  the  ganglion  cells  are  unipolar,  and  of  the 
same  nature  as  those  described  above,  each  being 
possessed  of  an  axis  cylinder  process,  which  becomes 


Fig.  95.— An  iso- 
lated Ganglion 
Cell  of  a  Spinal 
Ganglion  of 
Toad. 

The  axis  cylinder 
process  becomes 
transformed  into  a 
medullated  nerve- 
fibre.  The  capsule 
of  the  cell  is  pro- 
longed as  the  neu- 
rilemma of  the 
nerve-fibre.  (Key 
and  Retzius. ) 


i66 


Elements  of  Histology 


[Chap.  xx. 


soon   connected   with   a   nerve-fibre.       At   the   back 
of   the  tongue   there   are   similar   small   microscopic 


ganglia. 


CHAPTER   XX. 

THE    SYMPATHETIC    SYSTEM. 

223.  The  sympathetic  nerve-branches  are  of  exactly 
the  same  nature  in  their  connective  tissue  investments 
(epi-  peri-  and  endo-neurium),  and  in  the  arrangement 

'ill 
I 


Fig.  96.— Sympathetic  Nerves. 

nvested  in  an  endothelial  sheath 
hree  non-medullated  nerve-nbres  o: 
largest  shows  division ;  c,  two  varicose  nerve-fibres.    (Atlas.) 


A,  A  small  bundle  invested  in  an  endothelial  sheath  perineurium;  b,  one 
medullated  and  three  non-medullated  nerve-nbres  of  various  sizes;  the 


of  the  fibres  in  bundles  (Fig.  96,  a),  as  the  cerebro- 
spinal nerves.  Most  of  the  nerve-fibres  in  the  bundles 
are  non-medullated  or  Kemak's  fibres  (Fig.  96,  b),  each 


Chap.  XX.] 


The  Sympathetic  System. 


:67 


being  an  axis  cylinder  invested  in  a  neurilemma,  with 
oblong  nuclei  indicative  of  nerve  corpuscles.  But  there 
are  some  medullated  nerve-fibres  to  be  met  with  in 


Fig.  97.— A  group  of  Gang-lion  Cells  interposed  in  a  bundle  of  Sympa- 
thetic Nerve-fibres ;  from  the  Bladder  of  a  Rabbit.     (Handbook.) 


each  bundle,  at  least,  of  the  larger  nerve-trunks. 
These  in  some  cases  show  the  medullary  sheath  more 
or   less    discontinuous,   and   with  a   varicose  outline 


Fig.  98.  —A  small  collection  of  Ganglion  Cells  along  a  small  Bundle  of 
Sympathetic  Nerve-fibres  in  the  Bladder  of  the  Babbit. 

Each  ganglion  cell  possesses  a  capsrtle.    The  substance  of  the  ganglion  cell  is 
prolonged  as  the  axis  cylinder  of  a  nerve-fibre.    (Atlas.) 

(Fig.  96,  c),  owing  to  a  uniform  local  accumulation  of 
fluid  between  it  and  the  axis  cylinder.  The  small  or 
microscopic  bundles  of  nerve-fibres  have  an  endothelial 


i68 


Elements  of  Histology.        [Chap.  xx. 


(perineural)  sheath.     The  small  and  large   branches 
form  always  rich  plexuses. 

224.  In  connection  with  the  macroscopic  and 
microscopic  sympathetic  nerve-branches,  are  gang- 
lionic enlargements.  They  occur  in  some  organs  very 
numerously — e.g.,  alimentary  canal,   urinary   bladder 

(Fig.  97  and  Fig. 
98),  respiratory  or- 
gans— and  are  of 
all  sizes,  from  a 
few  ganglion  cells 
placed  between,  or 
laterally  to,  the 
nerve-fibres  of  a 
small  bundle,  to 
huge  oval,  spheri- 
cal, or  irregularly- 
shaped  masses  of 
ganglion  cells  placed 
in  the  course  of  a 
large  nerve-bundle, 
or  situated  at  the 
point  of  anastomo- 
sis of  two  or  more 
nerve-branches. 

The  ganglion 
cells  (Fig.  99)  are 
of  very  different 
sizes,  each  possess- 
ing a  large  oval  or 
spherical  nucleus 
with  one  or  two 
nucleoli.      Their 


Fig.  99.— Sympathetic  Ganglion  Cell  of  Man. 

The  ganglion  cell  is  multipolar;  each  process  re- 
ceiving a  neurilemma  from  the  capsule  of  the     d-iono     ia      <anliav»ir>al 
a  II  becomes  a  non-medullated  nerve-fibre.  onajju     is     opiicnuai 

or  oval,  flask- 
shaped,  club-shaped,  or  pear-shaped ;  they  possess 
either  one,   two,   or  more  processes,  being  uni-,   bi-, 


chap,  xx.]       The  Sympa  thetic  System. 


169 


or  multi-polar.  The  cell  is  invested  in  a  capsule  lined 
with  nucleated  cells,  both  being  continued  on  the  pro- 
cesses as  neurilemma  and  nerve  corpuscles  respectively. 
The  processes  of  the  ganglion  cells  are  all  axis 
cylinder  processes,  and  invested  in  the  neurilemma, 
thus  representing  non-medul- 
lated  nerve-fibres.  They  do  not 
become  as  a  rule  medullated. 

225.  In  the  frog  (Beale, 
Arnold)  and  also  in  some  few 
instances  in  the  mammal,  the 
sympathetic  ganglion  cell  gives 
off  one  straight  axis  cylinder 
process,  into  which  the  sub- 
stance of  the  ganglion  cell  is 
prolonged.  This  is  entwined 
by  a  thin  spiral  fibre  (Fig.  100), 
taking  its  origin  bv  two  or 
more  rootlets  from  the  ganglion 
cell  substance,  and  circling 
round  the  (thicker)  straight 
axis  cylinder  process.  A  single 
neurilemma  ensheathes  them 
both.  Soon  the  spiral  fibre 
leaves  the  axis  cylinder  process, 
becoming  invested  with  a 
medullary  sheath  and  its  own 
neurilemma,  thus  forming  a 
medullated  fibre,  whereas  the 
straight  axis  cylinder  continues 
its  course  as  a  non-medullated 
nerve-fibre  (Key  and  Retzius). 

226.  The  ganglia  in  connec- 
tion with  the  plexuses  of  nerve 
branches    of     the     heart,    the 
ganglia  in  the  plexus  of  non-medullated  nerve-fibres 
existing  between  the  longitudinal  and    circular   coat 


Fig.  100.— A  Sympathetic 
Ganglion  Cell  of  the  Frog1, 
showing  the  straight  pro- 
cess and  the  spiral  fibre  ; 
the  latter  becomes  a  me- 
dullated fibre.  (Key  and 
Eetzius.) 


170 


Elements  of  Histology. 


[Chap.  xx. 


of  the  external  muscular  coat  in  the  alimentary  canal, 
known  as  the  plexus  myentericus  of  Auerbach,  the 
ganglia  in  the  plexus  of  nerve  branches  of  the  sub- 


Fig.  101. — Plexus  of  fine  Sympathetic  Nerve-fibres,  with  Ganglionic 
Enlargements  in  the  Nodal  Points.  From  the  Plexus  of  Meissner 
in  the  Submucous  Tissue  of  the  Intestine. 

a,  Fine  nerve-fibres ;  6,  groups  of  ganglion  cells  interposed  between  the 
nerve-fibres. 


mucous  tissue  in  the  alimentary  canal,  and  known  as 
Meissner's  plexus  (Fig.  101),  the  ganglia  in  the  plexuses 
of  nerve  branches  in  the  outer  wall  of  the  bladder,  in 
the  bronchial  wall,  in  the  trachea,  the  ganglia  in  con- 
nection with  the  nerves  supplying  the  ciliary  muscle 
of  the  eye,  &c,  belong  to  the  sympathetic  system. 


Chap.  XXI.] 


171 


CHAPTER    XXI. 


TEETH. 

227.  A  human  tooth,  adult  and  milk-tooth,  consists 
(Fig.  102)i of  (a)  the  enamel  covering  the  crown,  (b)  the 
dentine  forming  the  real 
matrix  of  the  whole 
tooth,  and  surrounding 
the  pulp  cavity  both  of 
the  crown  and  fangs, 
and  (c)  the  cement,  or 
crusta  petrosa,  or  sub- 
stantia osteoidea.  This 
cement  covers  the  outside 
of  the  dentine  of  the 
fang  or  fangs,  in  the 
same  way  as  the  enamel 
covers  the  dentine  of  the 
crown.  The  crusta  pe- 
trosa is  covered  on  its 
outside  by  a  dense  fibrous 
tissue  acting  as  a  perios- 
teum to  it,  and  is  fixed 
by  it  to  the  inner  surface 
of  the  bone  forming  the 
wall  of  the  alveolar 
cavity. 

228.  The  enamel 
(Fig.  103)  consists  of 
thin  microscopic  pris- 
matic elements,  the 
enamel  prisms  placed 
closely,  and  extending  in 


Fig. 


Longitudinal       Section 


through  the  Prssrnolar  Tooth  of 
Cat. 

a,  Enamel:  5,  dentine  ;  c, crusta  petros.i ; 
e,  periosteum :  /,  bone  of  alveolus. 
(Waldeyer,  in  Strieker's  Manual.) 


172 


Elements  of  Histology.      [Chap.  xxi. 


a  vertical  direction  from  the  surface  to  the  dentine. 
When  viewed  in  transverse  section,  the  enamel  prisms 
appear  of  an  hexagonal  outline,  and  separated  by  a  very 
fine  interstitial  cement  substance.  The  outline  of  the 
enamel  prisms  is  not  straight,  but  wavy,  so  that  the 
prisms  appear  varicose.  The  prisms  are  aggregated 
into  bundles,  which  are  not  quite  parallel,  but  more 
or  less  slightly  cover  one  another.  On  a  longitudinal 
section  through  a  tooth,  the  appearance  of  alternate 


B 


Fig.  103. — Enamel  Prisma. 
A,  In  longitudinal  view  ;  b,  in  cross  section.    (Kolliker.) 


light  and  dark  stripes  in  the  enamel  is  thus  produced. 
Besides  this  there  are  seen  in  the  enamel  dark  hori- 
zontal curved  lines,  the  brown  parallel  stripes  of 
Retzius,  probably  due  to  inequalities  in  the  density  of 
the  enamel  prisms  produced  by  the  successive  forma- 
tion of  layers  of  the  enamel.  The  enamel  consists 
chiefly  of  lime-salts  :  phosphate,  carbonate,  and  fluorate 
of  calcium. 

In  young  teeth  the  free  surface  of  the  enamel 
is  covered  with  a  delicate  cuticle  (the  cuticle  of 
Nasmyth),  being  a  single  layer  of  non-nucleated 
scales.  In  adult  teeth  this  cuticle  is  wanting,  hav- 
ing been  rubbed  off. 

229.  The  dentine  is  the  essential  part  of  the  hard 


Chap.  XXI.] 


Teeth. 


i73 


substances  of  the  tooth.     It  forms  a  complete  invest- 
ment of  the  pulp  cavity  of  the  crown  and  fang,  being 
slightly   thicker   in    the 
former  than  in  the  latter 
region.     The   dentine   is 
composed  of  (Fig.  104) : 

(1)  a  homogeneous  ma- 
trix; this  is  a  reticular 
tissue  of  fine  fibrils  im- 
pregnated with  lime- 
salts,  and  thus  resem- 
bles the  matrix  of  bone  ; 

(2)  long  fine  canals,  the 
dentinal  canals  or  tubes 
passing  in  a  more  or  less 
spiral  manner,  and  ver- 
tically from  the  inner 
to  the  outer  surface  of 
the  dentine.  These  tubes 
are  branched;  they  open 
in  the  pidp  cavity  with 
their  broadest  part,  and 
become  finer  as  they 
approach  the  outer  sur- 
face of  the  dentine. 
Each  canal  is  lined  with 
a  delicate  sheath — the 
dentinal  sheath.  Inside 
the  tube  is  a  fibre,  the 
dentinal  fibre,  a  solid 
elastic  fibre  originating 
with  its  thickest  part 
at  the  pulp  side  of  the 
dentine  from  ceils  lining 

the  outer  surface  of  the  pulp,  and  called  odontoblasts. 

On  the  outer  surface  of  the  dentine,  both  in  the 

region  of  the  enamel  and  crusta  petrosa,  the  dentinal 


Fig.  104. — From  a  Section  through 
a  Canine  Tooth  of  Man. 

a,  Crusta  petrosa,  with  large  bone  cor- 
puscles; 6,  interglobular  substance; 
c,  dentinal  tubules.  (Waldeyer,  in 
Strieker's  Manual.) 


174  Elements  of  Histology.      [Chap!  xxt. 

tubes  pass  into  a  layer  of  intercommunicating  irregular 
branched  spaces,  the  interglobular  spaces  of  Czermak, 
or  the  granular  layer  of  Purkinje.  These  communicate 
with  spaces  existing  between  the  bundles  of  enamel 
prisms  of  the  crown,  as  well  as  with  the  bone  laminse 
of  the  crusta  petrosa  of  the  fang.  The  interglobular 
spaces  contain  each  a  branched  nucleated  cell.  The 
dentinal  fibres  anastomose  with  the  processes  of  these 
cells.  The  incremental  lines  of  Salter  are  lines  more 
or  less  parallel  to  the  surface,  owing  to  imperfectly  cal- 
cified dentine — the  interglobular  substance  of  Czermak. 
The  lines  of  Schreger  are  curved  lines  parallel  to  the 
surface,  and  due  to  the  optical  effect  of  simultaneous 
curvatures  of  dentinal  fibres. 

230.  The  cement  is  osseous  substance,  being 
lamellated  bone  matrix  with  bone  corpuscles.  These 
latter  are  larger  than  in  ordinary  bone. 

231.  The  pulp  is  richly  supplied  with  blood-vessels, 
forming  networks,  and  extending  chiefly  in  a  direction 
parallel  to  the  long  axis  of  the  tooth.  Numerous 
medullated  nerve-fibres  forming  plexuses  are  met 
with  in  the  pulp  tissue ;  on  the  outer  surface  of  the 
pulp  they  become  non-medullated  fibres,  and  probably 
ascend  in  the  dentinal  tubes.  The  matrix  of  the 
pulp  is  formed  by  a  transparent  network  of  richly 
branched  cells,  similar  to  the  network  of  cells  forming 
the  matrix  of  gelatinous  connective  tissue. 

232.  On  the  outer  surface  of  the  pulp — i.e.,  the 
one  in  contact  with  the  inner  surface  of  the  dentine — 
is  a  layer  of  nucleated  cells,  which  are  elongated, 
more  or  less  columnar.  These  are  the  odontoblasts 
proper.  Between  them  are  wedged  in  more  or  less 
spindle-shaped  nucleated  cells,  the  outer  or  distal  pro- 
cess of  which  passes  into  a  dentinal  fibre.  The  odonto- 
blasts proper  are  concerned  in  the  production  of  the 
dentinal  matrix,  according  to  some  by  a  continuous 
growth  of   the  distal  or  outer  part  of  the  cell  and 


Chap,  xx r.]  Teeth.  175 

a  petrification  of  this  increment,  according  to  others 
by  a  secretion  by  the  cell  of  the  dentinal  matrix. 
Waldeyer,  Tomes,  and  others,  consider  the  odontoblasts 
proper  concerned  in  the  production  both  of  the  dentinal 
matrix  and  dentinal  fibres.  The  odontoblasts  proper 
and  the  spindle-shaped  cells  are  continuous  with  the 
branched  cells  of  the  pulp  matrix. 

2 3 3. Development  of  teeth. — The  first  rudi- 
ment of  a  tooth  in  the  embryo  appears  as  early  as  the 
second  month.  It  is  a  solid  cylindrical  prolongation  of 
the  stratified  epithelium  of  the  surface  into  the  depth 
of  the  embryonal  mucous  membrane.  Along  the 
border  of  the  jaws  the  epithelium  appears  thickened, 
and  the  subjacent  mucous  membrane  forms  there  a 
depression — the  'primitive,  dental  groove.  Into  this 
groove  the  solid  cylindrical  prolongation  of  the  surface 
epithelium  takes  place.  This  prolongation  represents 
the  rudiment  of  the  enamel  organ.  While  con- 
tinuing to  grow  in  the  depth,  it  soon  broadens  at  its 
deepest  part,  and  the  surrounding  vascular  mucous 
membrane  condenses  at  the  bottom  of  the  prolongation 
as  the  rudiment  of  the  tooth  papilla.  While  the  distal 
part  of  the  enamel  organ  continues  to  grow  towards  the 
depth,  it  gradually  embraces  the  tooth  papilla  in  the 
shape  of  a  cap — the  enamel  cap.  During  this  time  the 
connection  between  the  surface  epithelium  and  the 
enamel  cap  becomes  greatly  thinned  out  and  pushed 
to  one  side,  owing  to  the  growth  of  the  enamel  cap  and 
papilla  taking  place  chiefly  to  one  side  of  the  original 
dental  groove. 

234.  The  enamel  cap  (Fig.  105)  is  composed  of 
three  strata — an  inner,  middle,  and  outer  stratum. 
The  inner  stratum  is  the  layer  of  the  enamel  cells  ;  it 
is  a  layer  of  beautiful  columnar  epithelial  cells ;  they 
were  originally  continuous  with  the  deep  layer  or  the 
columnar  cells  of  the  surface  epithelium.  The  middle 
stratum  is  the  thickest  and  is  of  great  transparency, 


176 


Elements  of  Histology.       [chap.  xxi. 


owing  to  a  transformation  of  the  middle  layer  of  the 
epithelial  cells  into  a  spongy  gelatinous  tissue,  due  to 
accumulation  of  fluid  between  the  epithelial  cells 
of  this  layer,  and  to  a  reduction  of  its  substance 
to  thin  nucleated  plates,  apparently  branched.     The 


Fig.  105. 


-From  a  Section  through  the  Tooth  and  Lower  Jaw 
of  Foetal  Kitten. 


a,  Epithelium  of  the  free  surface  of  the  gum  ;  6,  the  mucous  membrane  of  same ; 
c,  spongy  bone  of  jaw;  d,  papilla  of  tooth;  e,  odontoblasts;  /,  dentine;  g, 
enamel ;  h,  membrane  of  Nasmyth  ;  i,  enamel  cells ;  j,  middle  layer  of  enamel 
organ ;  k,  outer  layer  of  enamel  organ. 


outer  stratum  consists  of  one  or  more  layers  of 
polyhedral  cells,  continuous  with  the  deep  layers  of 
cells  of  the  epithelium  of  the  surface  of  the  gum. 
Outside  the  enamel  cap  is  the  gelatinous  vascular 
tissue  of  the  mucous  membrane  of  the  gum. 

235.  The  foetal  tooth  papilla  is  a  vascular  embryo- 
nal or  gelatinous  tissue ;  on  its  outer  surface  a  con- 


Chap,  xxi.]  Teeth*  177 

densation  of  its  cells  is  soon  noticeable  into  a  more  or 
less  continuous  stratum  of  elongated  or  columnar  cells, 
the  odontoblasts. 

236.  The  dentine  is  formed  in  connection  with 
the  odontoblasts  (Fig.  105) ;  on  its  outside  appears  the 
enamel  formed  by  the  enamel  cells,  i.e.,  the  inner 
layer  of  the  enamel  organ.  The  dentine  and  enamel 
are  deposited  gradually,  and  in  layers.  At  first  they 
are  soft  tissues,  showing  a  vertical  differentiation 
corresponding  to  the  individual  cells  of  the  enamel 
cells  and  odontoblasts  respectively.  Soon  lime  salts 
are  deposited  in  it,  at  first  imperfectly,  but  afterwards 
a  perfect  petrifaction  takes  place.  The  layer  of  most 
recently  formed  enamel  and  dentine  is  more  or  less 
distinctly  marked  off  from  the  more  advanced  layer, 
the  most  recently  formed  layer  of  the  enamel  being 
situated  next  to  the  enamel  cells,  that  of  the  dentine 
next  to  the  odontoblasts. 

The  milk  tooth  remains  buried  in  the  mucous 
membrane  of  the  gum.  When  it  breaks  through,  the 
enamel  remains  covered  with — i.e.,  carries  with  it — 
the  inner  stratum  of  the  enamel  organ  only,  i.e.,  the 
enamel  cells  (Fig.  105,  h) ;  these  at  the  same  time  as 
the  surface  of  the  enamel  increases  become  much 
flattened,  and,  finally  losing  their  nuclei,  are  con- 
verted into  a  layer  of  transparent  scales,  the  membrane 
or  cuticle  of  Nasmytk. 

237.  Long  before  the  milk  tooth  breaks  through 
the  gum,  there  appears  a  solid  cylindrical  mass  of 
epithelial  cells  extending  into  the  depth  from  the 
connection  between  the  enamel  organ  and  the  epithe- 
lium of  the  surface  of  the  gum  mentioned  above. 
This  epithelial  outgrowth  represents  the  germ  for 
the  enamel  organ  of  the  permanent  tooth ;  but  it 
remains  stationary  in  its  growth  till  the  time  arrives 
for  the  milk  tooth  to  be  supplanted  by  a  permanent 
tooth.     Then  that   rudiment    undergoes   exactly  the 

M 


178 


Elements  of  Histology.     [Chap.  xxn. 


same  changes,  of  growth  as  the  enamel  organ  of  the 
milk  tooth  did  in  the  first  period  of  foetal  life.  A 
new  tooth  is  thus  formed  in  the  depth  of  the  alveolar 
cavity  of  a  milk  tooth,  and  the  growth  of  the  former 
in  size  and  towards  the  surface  gradually  lifts  the 
latter  out  of  its  socket. 


CHAPTER  XXII. 

THE      SALIVARY      GLANDS. 

238.    The    salivary   glands,    according    to    their 

structure  and  secretion,  are  of  the  following  kinds  : — 

(1)   True  salivary  (Fig.  106),  serous,  or  albuminous 


Fig.  106.— From  a  Section  through  a  Serous  or  True  Salivary  Gland ; 
part  of  the  Human  Sub-maxillary. 

a.  The  gland  alveoli,  lined  with  the  albuminous"  salivary  cells  ;"  b,  intralobular 
duct  cut  transversely.    (Atlas.) 


chap,  xxii.]       The  Salivary  Glands. 


179 


glands,  such  as  the  parotid  of  man  and  mammals, 
the  sub-maxillary  and  orbital  of  rabbit,  the  sub- 
maxillary of  the  guinea-pig.  They  secrete  true,  thin, 
watery  saliva. 

(2)  Mucous  glands,  such  as  the  sub-maxillary  and 
orbital  of   cat  and   dog    (Fig.    107),   the  sub-lingual 


Fig.  107.— From  a  Section  through  the  Orbital  (mucous)  Gland 
of  Dog.     Quiescent  state. 

The  alveoli  are  lined  with  transparent  "  raucous  cells,"  and  outside 
these  are  the  demilunes  of  Heidenhain.    (Heidenhain.) 


of  cat,  dog,  rabbit,  and  guinea-pig.  They  secrete 
thickish,  less  watery  mucus. 

(3)  Mixed  salivary,  or  muco -salivary  glands,  such  as 
the  sub-maxillary  and  sub-lingual  of  man  and  ape. 

In  addition  to  the  three  salivary  glands — parotid, 
sub-maxillary,  and  sub-lingual — there  are  in  some 
cases,  as  in  the  rabbit  and  the  guinea-pig,  two  minute 
additional  glands,  one  intimately  annexed  to  the 
parotid  and  the  other  to  the  sub-maxillary,  and  of  the 
nature  of  a  mucous  gland.  These  are  the  superior  and 
inferior  ad  maxillary  glands. 


180  Elements  of  Histology.      [Chap.  xxii. 

239.  The  framework.— Each  salivary  gland 
is  enveloped  in  a  fibrous  connective  tissue  capsule, 
in  connection  with  which  are  fibrous  trabecule  and 
septa  in  the  interior  of  the  gland,  by  which  the  sub- 
stance of  the  latter  is  subdivided  into  lobes,  these 
again  into  lobules,  and  these  finally  into  the  alveoli 
or  acini.  The  duct,  large  vessels  and  nerves  pass 
to  and  from  the  gland  by  the  hilum.  The  con- 
nective tissue  is  of  loose  texture,  contains  elastic 
fibres,  and,  in  some  instances  more,  in  others  less, 
numerous  lymphoid  cells.  In  the  sub-lingual  gland 
they  are  so  numerous  that  they  form  continuous  rows 
between  the  alveoli.  The  connective  tissue  matrix 
between  the  alveoli  is  chiefly  represented  by  fine 
bundles  of  fibrous  tissue,  and  branched  connective 
tissue  corpuscles. 

240.  The  ducts. — Following  the  chief  duct  of 
the  gland  through  the  hilum  into  the  interior,  we  see 
that  it  divides  into  several  great  branches,  according 
to  the  number  of  lobes ;  each  of  these  breaks  off 
into  several  branches,  one  for  each  lobule.  Entering 
the  lobule  the  duct  has  become  very  minute,  and 
passing  along  it  gives  off  laterally  several  minute  ducts, 
all  within  the  lobule  being  the  intralobular  ducts, 
or  the  salivary  tubes  of  Pfluger,  the  bigger  ducts 
being  the  interlobular,  and,  further,  the  interlobar 
ducts.  Each  of  the  latter  consists  of  a  limiting 
membrana  propria,  strengthened,  according  to  the 
size  of  the  duct,  by  thicker  or  thinner  trabecule  of 
connective  tissue.  In  the  chief  branches  there  is  pre- 
sent in  addition  non-striped  muscular  tissue.  The 
interior  of  the  duct  is  a  cavity  lined  with  a  layer  of 
columnar  epithelial  cells.  In  the  largest  branches  there 
is,  outside  this  layer  and  inside  the  membrana  propria, 
a  layer  of  small  polyhedral  cells. 

241.  The  intralobular  ducts,  or  the  salivary 
tubes    of    Pfluger,   consist   of    a    limiting    membrana 


Chap,  xxii.]       The  Salivary  Glands.  181 

propria,  with  a  single  layer  of  columnar  epithelial  cells. 
Each  of  these  has  a  spherical  nucleus  in  about  the 
middle  ;  the  outer  half  of  the  cell  substance  shows  very 
marked  longitudinal  striation,  due  to  more  or  less  coarse 
nbrilhe  (see  Fig.  106).  The  inner  half,  i.e.,  the  one 
bordering  the  lumen  of  the  duct,  is  only  very  faintly 
striated.  The  outline  of  these  salivary  tubes  is  never 
smooth,  but  irregular,  hence  the  diameter  of  the  tube 
varies  from  place  to  place. 

Not  in  all  salivary  glands  do  the  epithelial  cells 
of  the  intralobular  ducts  show  this  coarse  fibrillation 
in  the  outer  part  of  their  substance ;  e.g.,  it  is  not 
present  in  the  sub-lingual  gland  of  the  dog  and  guinea- 

Pig- 

242.   The    ends    of    the   branches  of  the   salivary 

tubes  are  connected  with  the  secreting  parts  of  the 
lobule,  i.e.,  the  acini  or  alveoli.  These  always  very 
conspicuously  differ  in  structure  from  the  salivary 
tubes,  and,  as  a  rule,  are  larger  in  diameter.  That 
part  of  the  duct  which  is  in  immediate  connection  with 
the  alveoli  is  the  intermediary  part,  this  being  inter- 
posed, as  it  were,  between  the  alveoli  and  the  salivary 
tube  with  fibrillated  epithelium.  The  intermediary  part 
is  much  narrower  than  the  salivary  tube,  and  is  lined 
with  a  single  layer  of  very  flattened  epithelial  cells, 
each  with  a  single  oval  nucleus  ;  the  boundary  is 
formed  by  the  membrana  propria,  continued  from  the 
salivary  tube.  The  lumen  of  the  intermediary  part  is 
much  smaller  than  that  of  the  salivary  tube,  and  is 
generally  lined  with  a  fine  hyaline  membrane,  with 
here  and  there  an  oblong  nucleus  in  it. 

At  the  point  of  transition  of  the  salivary  tube 
into  the  intermediary  part  there  is  generally  a  sudden 
diminution  in  size  of  the  former,  and  the  columnar 
cells  of  the  salivary  tube  are  replaced  by  polyhedral 
cells  ;  this  is  the  neck  of  the  intermediary  part.  In 
some  salivary   glands,    especially  in  the  mucous,  this 


1 82  Elements  of  Histology,     [Chap.  xxu. 

neck  is  the  only  portion  of  the  intermediary  part 
present,  e.g.,  in  the  sub-maxillary  and  orbital  glands 
of  dog  and  cat,  and  in  the  sub-lingual  of  the  rabbit. 
In  others,  especially  in  the  serous  salivary  glands,  as 
in  the  parotid  of  man  and  mammals,  sub-maxillary  of 
rabbit  and  guinea-pig,  and  in  the  mixed  salivary — 
e.g.,  sub-maxillary  and  sub-lingual  of  man  and  ape — 
there  exists  after  the  neck  a  long  intermediary  part, 
which  gives  off  several  shorter  or  longer  branches  of 
the  same  kind,  all  of  which  terminate  in  alveoli. 

243.  The  alveoli  or  acini  are  the  essential 
or  secreting  part  of  the  gland  ;  they  are  fiask-shaped, 
club-shaped,  shorter  or  longer  cylindrical  tubes,  more 
or  less  wavy,  or  if  long,  more  or  less  convoluted ; 
many  of  them  are  branched.  Generally  several  open 
into  the  same  intermediary  part  of  a  salivary  tube. 
The  alveoli  are  much  larger  in  diameter  than  the 
intermediary  part,  and  slightly  larger,  or  about  as 
large,  as  the  intralobular  ducts.  But  there  is  a 
difference  in  this  respect  between  the  alveoli  of  a 
serous  and  a  mucous  salivary  gland ;  in  the  former 
the  alveoli  are  smaller  than  in  the  latter. 

The  membrana  propria  of  the  intermediary  duct 
is  continued  as  the  membrana  propria  of  the  alveoli. 
This  is  a  reticulated  structure,  being  in  reality  a  basket- 
shaped  network  of  hyaline  branched  nucleated  cells 
(Boll).  The  lumen  of  the  alveoli  is  very  minute  in 
the  serous,  but  is  considerably  larger  in  the  mucous 
glands ;  it  is  in  both  glands  smaller  during  secretion 
than  during  rest. 

244.  The  epithelial  cells  lining  the  alveoli  are 
called  the  salivary  cells  —  they  are  of  different 
characters  in  the  different  salivary  glands,  and  chiefly 
determine  the  nature  of  the  gland.  The  cells  are 
separated  from  one  another  by  a  fluid  albuminous 
cement  substance.  (1)  In  the  serous  or  true  salivary 
glands,  as  parotid  of  man  and  mammals,  sub-maxillary 


chap,  xxii.]       The  Salivary  Glands.  183 

of  rabbit  and  guinea-pig,  the  salivary  cells  form  a 
single  layer  of  shorter  or  longer  columnar  or  pyra- 
midal albuminous  cells,  composed  of  a  densely  reticu- 
lated protoplasm,  and  containing  a  spherical  nucleus  in 
the  outer  part  of  the  cell.  (2)  In  the  mucous  glands, 
such  as  the  sub-lingual  of  the  guinea-pig,  or  the 
admaxillary  of  the  same  animal,  the  cells  lining  the 
alveoli  form  a  single  layer  of  goblet-shaped  mucous 
cells,  such  as  have  been  described  in  par.  25.  Each 
cell  consists  of  an  inner  principal  part,  composed  of  a 
transparent  mucoid  substance  (contained  in  a  wide- 
meshed  reticulum  of  the  protoplasm),  and  an  outer 
small,  more  opaque  part,  containing  a  compressed  and 
flattened  nucleus.  This  part  is  drawn  out  in  a  fine 
extremity,  which,  being  curved  in  a  direction  parallel 
to  the  surface  of  the  alveolus,  is  imbricated  on  its 
neighbours. 

245.  In  the  case  of  the  sub-maxillary  and  orbital 
glands  of  the  dog,  the  sub-lingual  of  rabbit,  there  exist, 
in  addition  to,  and  outside  of  the  mucous  cells  lining 
the  alveoli,  but  within  the  membrana  propria,  from 
place  to  place  crescentic  masses,  being  the  demilunes 
of  Heidenhain,  or  the  crescents  of  Gianuzzi  (see  Pig. 
107).  Each  is  composed  of  several  polyhedral  granu- 
lar-looking cells,  each  with  a  spherical  nucleus ;  the 
cells  at  the  margin  of  the  crescent  are  of  course 
thinner  than  those  forming  the  middle.  Heiden- 
hain  and  his  pupils,  Lavdovski  and  others,  have 
shown  that,  during  prolonged  exhausting  stimula- 
tion of  the  sub-maxillary  and  orbital  of  the  dog, 
all  the  lining  cylindrical  mucous  cells  become  re- 
placed by  small  polyhedral  cells,  similar  to  those 
constituting  the  crescents,  while  at  the  same  time 
the  alveoli  become  smaller  (Fig.  108).  These  ob- 
servers maintain  that  this  change  is  due  to  a  total 
destruction  of  the  mucous  cells,  and  a  replacement 
of   them    by   new    ones,    derived    by   multiplication 


1 84 


Elements  of  Histology.      [Chap.  xxn. 


from  the  crescent  cells.  This  is  improbable,  since, 
during  ordinary  conditions  of  secretions,  there  is  no 
disappearance  of  the  mucous  cells  as  such  ;  they  change 

in  size,  be- 
coming larger 
during  secre- 
tion, and  their 
contents  are 
converted  into 
perfect  mucus. 
It  is  probable 
that,  on  pro- 
longed exhaus- 
tive stimula- 
tion, the  mucous 
cells  collapse 
into  the  small 
cells,  seen  by 
Heidenhain  and 
his  pupils. 

246.  The 
alveoli  of  the 
sub -lingual  of 
the  dog  are  again  different  in  structure  both  from  those 
of  the  sub-maxillary  of  the  dog  and  of  the  sub-lingual 
of  guinea-pig,  for  the  alveoli  are  there  lined  either 
with  mucous  cells  or  with  columnar  albuminous 
cells,  or  the  two  kinds  of  cells  follow  one  another 
in  the  same  alveolus. 

This  gland  is  a  sort  of  intermediate  form  be- 
tween the  sub-lingual  of  man  and  the  sub-maxillary 
of  man  and  ape,  i.e.,  the  mixed  or  muco-salivary 
glands.  In  these  the  great  number  of  alveoli  are 
serous,  i.e.,  small,  with  small  lumen,  and  lined  with 
albuminous  cells,  whereas  there  are  always  present 
a  few  alveoli  exactly  like  those  of  a  mucous  gland. 
The  two  kinds  of  alveoli  are  in  direct  continuity  with 


Fig.  103. — From  a  Section  through  the  Orbital 
Gland  of  Dog,  after  prolonged  electrical 
stimulation. 

The  alveoli  are  lined  with  small  granular  cells. 
(Lavdovski.) 


cup.  xxn.j       The  Salivary  Glands. 


185 


one  another.  In  some  conditions  there  are  only  very 
few  mucous  alveoli  to  be  met  with  within  the  lobule, 
so  few  sometimes  that  they  seem  to  be  altogether 
absent ;  in  others  they  are  numerous,  but  even  under 
most  favourable  conditions  form  only  a  fraction  of  the 
number  of  the  serous  alveoli.  In  the  sub- lingual  of 
man  they  are  much  more  frequent,  and  for  this  reason 
this  gland  possesses  a  great  resemblance  to  the  sub- 
lingual of  the  dog. 

What  appear  to  be  crescents  in  the  mucous  alveoli 


Pig.  109.— Alveoli  of  Serous  Gland. 
a,  At  rest ;  b,  first  stage  of  secretion ;  c,  prolonged  secretion.   (Langley.) 


of  the  human  gland  are  an  oblique  view  of  albuminous 
cells  lining  the  alveoli  at  the  transition  between  the 
mucous  and  serous  part  of  the  same  gland-tube. 

247.  The  columnar  salivary  cells  lining  the  alveoli 
of  the  sub-maxillary  of  the  guinea-pig  in  some  condi- 
tions show  two  distinct  portions,  an  outer  homogeneous 
or  slightly  and  longitudinally  striated  substance,  and 
an  inner,  more  transparent,  granular-looking  part,  and 
in  this  respect  the  cells  resemble  those  of  the  pancreas. 
(See  a  future  chapter.) 

Langley  has  shown  (Fig.  109)  that  during  the 
period  preparatory  to  secretion  the  cells  lining  the 
alveoli  of  the  serous  salivary  glands  become  enlarged 


1 86  Elements  of  Histology.     [Ghap.  xxii. 

and  filled  with  coarse  granules ;  during  secretion 
these  granules  become  used  up,  so  that  the  cell- 
substance  grows  more  transparent,  beginning  from  the 
outer  part  of  the  cell  and  gradually  progressing  to- 
wards the  lumen  of  the  alveolus. 

248.  Blood-vessels  and  lymphatics.—  The 
lobules  are  richly  supplied  with  blood-vessels.  The 
arteries  break  up  into  numerous  capillaries,  which 
with  their  dense  networks  surround  and  entwine  the 
alveoli.  Between  the  interalveolar  connective  tissue 
carrying  the  capillary  blood-vessels  and  the  membrana 
propria  of  the  alveoli  exist  lymph  spaces  surrounding 
the  greater  part  of  the  circumference  of  the  alveoli 
and  forming  an  intercommunicating  system  of  spaces. 
They  open  into  lymphatic  vessels  accompanying  the 
intralobular  ducts,  or  at  the  margin  of  the  lobule 
directly  empty  themselves  into  the  interlobular 
lymphatics.  The  connective  tissue  between  the  lobes 
contains  rich  pleocuses  of  lymphatics. 

249.  The  nerve-branches  form  plexuses  in 
the  interlobular  tissue.  In  connection  with  them  are 
larger  or  smaller  ganglia.  They  are  very  numerously 
met  with  in  the  sub-maxillary,  but  are  absent  in  the 
parotid.  Some  ganglia  are  present  in  connection  with 
the  nerve-branches  surrounding  the  chief  duct  of  the 
sub-lingual  gland. 

Pfluger  maintains  that  the  ultimate  nerve-fibres 
are  connected  with  the  salivary  cells  of  the  alveoli 
in  man  and  mammals,  but  this  remains  to  be  proved. 


Chap.  XXIII.]  187 


CHAPTER    XXIII. 

THE    MOUTH,    PHARYNX,    AND    TONGUE. 

250.  The  glands.— Into  the  cavity  of  the 
mouth  and  pharynx  open  very  numerous  minute 
glands,  which,  as  regards  structure  and  secretion,  are 
either  serous  or  mucous.  The  latter  occur  in  the 
depth  of  the  mucous  membrane  covering  the  lips  of  the 
mouth,  in  the  buccal  mucous  membrane,  in  that  of  the 
hard  palate,  and  especially  in  that  of  the  soft  palate 
and  the  uvula,  in  the  depth  of  the  mucous  membrane 
of  the  tonsils,  at  the  back  of  the  tongue,  and  in  the 
mucous  membrane  of  the  pharynx.  The  serous  glands 
are  found  in  the  back  of  the  tongue,  in  close  proximity 
to  the  parts  containing  the  special  organs  for  the 
perception  of  taste — the  taste  goblets  or  buds  (see 
below.)  All  glands  are  of  very  minute  size,  but 
when  isolated  they  are  perceptible  to  the  unaided  eye 
as  minute  whitish  specks,  as  big  as  a  pin's  head,  or 
bigger.  The  largest  are  in  the  lips,  at  the  back  of 
the  tongue  and  soft  palate,  where  there  is  something 
like  a  grouping  of  the  alveoli  around  the  small  branches 
of  the  duct,  so  as  to  form  little  lobules. 

251.  The  chief  duct  generally  opens  with  a  narrow 
mouth  on  the  free  surface  of  the  oral  cavity ;  it 
passes  in  a  vertical  or  oblique  direction  through  the 
superficial  part  of  the  mucous  membrane.  In  the 
deeper,  looser  part  (submucous  tissue)  it  branches 
in  two  or  more  small  ducts,  which  take  up  a  number 
of  alveoli.  Of  course,  on  the  number  of  minute  ducts 
and  alveoli  depends  the  size  of  the  gland. 

In  man,  all  ducts  are  lined  with  a  single  layer  of 
columnar  epithelial   cells,   longer  in  the  larger  than 


i88 


Elements  of  Histology.    [Chap.  xxm. 


in  the  smaller  ducts ;  in  mammals,  the  epithelium 
is  a  single  layer  of  polyhedral  cells.  No  fibrillation 
is  noticeable  in  the  epithelial  cells.  At  the  transition 
of  the  terminal  ducts  into  the  alveoli  there  is  occasion- 
ally a  slight  enlargement,  called  the  infundibulum ; 

here     the     granular- 


looking 
cells     of 
change 


lining 


epithelial 

the     duct 

into       the 

columnar  transparent 

mucous    cells 

the  alveoli. 

252.  The  alveoli 
of  these  glands  are 
identical  with  those 
of  the  mucous  glands 
described  above  (Fig. 
110) — e.g.,  the  sub- 
lingual gland,  as  re- 
gards size,  tubular 
branched  nature,  the 
lining  epithelium,  and 
lumen. 

In  some  instances 
(as  in  the  soft  palate 
and  tongue)  the  duct 
near  the  opening  is 
lined  with  ciliated 
columnar  epithelium. 
The  stratified  epithe- 
lium of  the  surface  is  generally  continued  a  short  dis- 
tance into  the  mouth  of  the  duct. 

253.  The  serous  glands  at  the  root  of  the 
tongue  (von  Ebner)  differ  from  the  mucous  chiefly 
in  the  size,  epithelium,  and  lumen  of  the  alveoli. 
These  are  of  exactly  the  same  nature  and  structure 
as  those  of  the  serous  or  true  salivary  glands. 


Fig.  110.— Part  of  a  Lobule  of  a  Mucous 
Gland  in  the  Tongue  of  Dog. 

a,  Gland  tubes  (alveoli)  viewed  in  various 
directions  ;  they  are  lined  with  transparent 
'*  mucous  cells;"  d,  duct,  lined  with  small 
polyhedral  cells.    (Atlas.) 


Chap,  xxiii.]  Mouth,  Pharynx,  and  Tongue.      189 

Saliva,  obtained  from  the  mouth  contains  num- 
bers of  epithelial  scales,  detached  from  the  surface 
of  the  mucous  membrane,  groups  of  bacteria  and 
micrococci,  and  lymph  corpuscles.  Some  of  these  are 
in  a  state  of  disintegration,  while  others  are  swollen 
up  by  the  water  of  the  saliva.  In  these  there  are 
contained  numbers  of  granules  in  rapid  oscillation, 
called  Brownian  molecular  movement. 

254.  The  mucous  membrane  lining  the  cavity 
of  the  mouth  is  a  thin  membrane  covered  on  its  free 
surface  with  a  thick  stratified  pavement  epithelium, 
the  most  superficial  cells  being  scales,  more  or  less 
hornified. 

Underneath  the  epithelium  is  a  somewhat  dense 
feltwork  of  fibrous  connective  tissue,  with  numerous 
elastic  fibrils  in  networks.  This  part  is  the  mucosa, 
and  it  projects  into  the  epithelium  in  the  shape  of 
cylindrical  or  conical  papillce. 

According  to  the  thickness  of  the  epithelium,  the 
papillae  differ  in  length.  The  longest  are  found  where 
the  epithelium  is  thickest — e.g.,  in  the  mucosa  of  the 
lips,  soft  palate,  and  uvula. 

Numerous  lymph  corpuscles  are  found  in  the 
mucosa  of  the  palate  and  uvula.  Sometimes  they 
amount  to  diffuse  adenoid  tissue.  The  deeper  part  of 
the  mucous  membrane  is  the  submucosa.  It  is  looser  in 
its  texture,  but  it  is  also  composed  of  fibrous  connec- 
tive tissue  with  elastic  fibrils.  The  glands  are  here 
embedded ;  fat  tissue  in  the  shape  of  groups  of  fat 
cells  up  to  continuous  lobules  of  fat  cells  are  here  to 
be  met  with.  The  large  vascular  and  nervous  trunks 
pass  to  and  from  the  submucosa. 

255.  Striped  muscular  tissue  is  found  in  the 
submucosa.  Of  the  lips,  soft  palate,  uvula,  and  pala- 
tine arches,  it  forms  a  very  conspicuous  portion — 
e.g.,  musculus  sphincter  orbicularis,  with  its  outrunners 
into  the  mucous  membrane  of  the  lip,  the  muscles  of 


1 90  Elements  of  Histology,    [chap.  xxm. 

the  palate,  uvula  (levator  and  tensor  palati),  and  the 
arcus,  palato-pharyngeus,  and  palato-glossus. 

256.  The  last  branches  of  the  arteries  break  up  in 
a  dense  capillary  network  on  the  surface  of  the  mucosa, 
and  from  it  loops  ascend  into  the  papillae.  Of 
course,  fat  tissue,  glands,  and  muscular  tissue  re- 
ceive their  own  supply.  There  is  a  very  rich  plexus 
of  veins  in  the  superficial  part  of  the  mucosa.  They  are 
conspicuous  by  their  size  and  the  thinness  of  their  wall. 

The  lymphatics  form  networks  in  all  layers  of  the 
mucosa,  including  the  papillae.  The  large  efferent 
trunks  are  situated  in  the  submucosa.  The  last 
outrunners  of  the  nerve  branches  form  a  plexus  of  non- 
medullated  fibres  in  the  superficial  layer  of  the  mucosa, 
whence  numerous  primitive  fibrillce  ascend  into  the 
epithelium  to  form  networks.  Meissner's  tactile  cor- 
puscles have  been  found  in  the  papillae  of  the  lips  and 
in  those  of  the  tongue. 

257.  In  the  pharynx  the  relations  remain  the 
same,  except  in  the  upper  or  nasal  part,  where 
we  find  numerous  places  covered  with  columnar 
ciliated  epithelium.  As  in  the  palatine  tonsils  so 
also  here,  the  mucosa  is  infiltrated  with  diffuse 
adenoid  tissue,  and  with  lymph  follicles  in  great 
numbers.     This  forms  the  pharynx  tonsil  of  Luschka. 

In  the  palatine  tonsil  and  in  the  pharynx  tonsil 
there  are  numerous  crypts  leading  from  the  sur- 
face into  the  depth.  This  is  due  to  the  folding  of 
the  infiltrated  mucosa.  Such  crypts  are,  in  the 
pharynx,  sometimes  lined  all  through  with  ciliated  epi- 
thelium, although  the  parts  of  the  free  surface  around 
them  are  covered  with  stratified  pavement  epithelium. 

258.  The  tongue  is  a  fold  of  the  mucous 
membrane.  Its  bulk  is  made  up  of  striped  muscular 
tissue  (genio-,  hyo-,  and  stylo-glossus  ;  according  to 
direction  :  longitudinalis  superior  and  inferior,  and 
transversus  linguae).      The  lower  surface  is  covered 


chap,  xxiii.]  Mouth,  Pharynx,  and  Tongue.      191 

with  a  delicate  mucous  membrane,  identical  in  struc- 
ture with  that  lining  the  rest  of  the  oral  cavity, 
whereas  the  upper  part  is  covered  with  a  mem- 
brane, of  which  the  mucosa  projects  over  the  free 
surface  as  exceedingly  numerous  fine  and  short  hair- 
like processes,  the  papillce  filiformes,  or  as  less  nume- 
rous isolated  somewhat  longer  and  broader  mushroom  - 
shaped  papillce  fungiformes.  The  papillae,  as  well  as 
the  pits  between  them,  are  covered  with  stratified 
pavement  epithelium.  Each  has  numbers  of  minute 
secondary  papillae.  Their  substance,  like  the  mucous 
membrane  of  the  tongue,  is  made  up  of  fibrous 
connective  tissue.  This  is  firmly  and  intimately 
connected  with  the  fibrous  tissue  forming  the  septa 
between  the  muscular  bundles  of  the  deeper  tissue. 
The  mucous  membrane  is  on  the  whole  thin.  It 
contains  large  vascular  trunks,  amongst  which  the 
plexus  of  veins  is  very  conspicuous.  On  the  surface 
of  the  mueosa  is  a  rich  network  of  capillary  blood- 
vessels, extending  as  complex  loops  into  the  papillae. 
Lymphatics  form  rich  plexuses  in  the  mucosa  and 
in  the  deep  muscular  tissue.  Fat  tissue  is  common 
between  the  muscular  bundles,  especially  at  the  back 
of  the  tongue. 

259.  There  are  two  varieties  of  glands  present 
in  the  tongue,  the  mucous  and  serous.  The  latter 
occur  only  at  the  back,  and  in  the  immediate 
neighbourhood  of  the  taste  organs ;  the  mucous 
glands  are  chiefly  present  at  the  back;  but  in 
the  human  tongue  there  are  small  mucous  glands 
(glands  of  ISTuhn)  in  the  tip.  All  the  glands  at 
the  back  are  embedded  between  the  bundles  of 
striped  muscular  tissue,  and  thus  the  movements 
of  the  tongue  have  the  effect  of  squeezing  out  the 
secretion  of  the  glands.  Near  and  about  the  glands 
numerous  nerve  bundles  are  found  connected  with 
minute  ganglia. 


192 


Elements  of  Histology.    [Chap.  xxm. 


At  the  root  of  the  tongue  the  mucous  membrane 
is  much  thicker,  and  contains  in  its  mucosa  numerous 
lymph    follicles    and    diffuse   adenoid   tissue.      Thus 


'.in  l 


Tig.  111. — From  a  Vertical  Section  through  a  Circumvallate  Papilla 
of  the  Tongue  of  a  Child. 

o.The  stratified  pavement  epithelium  covering  the  fold  around  the  papilla; 
6,  the  mucous  membrane  ;  s,  the  serous  glands ;  g,  the  pit  between  the  fold 
and  the  papilla ;  in  the  epithelium  of  this  latter  are  seen  the  "taste  goblete." 
(Atlas.) 

numerous  knob-like  or  fold  like  prominences  of  the 
mucosa  are  produced.  There  are  also  minute  pits  or 
crypts  leading  into  the  depth  of  these  prominences. 

260.  The  papillae  circumvallatse  (Fig.  Ill) 
are  large  papillae  fungiformes,  each  surrounded  by  a  fold 
of  the  mucosa.     They  contain  taste  goblets  or  buds — 


Chap,  xxiii.]  Mouth,  Pharynx,  and  Tongue.       19; 


i.e.. 


the  terminal  taste  organs 


tongue,  in  the  region  of 


At  the  margin 


of  the 
the  circumvallate  papillae, 


there  are  always  a  few  permanent  folds,  which  also 
contain  taste  goblets.  In  some  domestic  animals 
these  folds  assume  a  definite  organisation — e.g.,  in  the 
rabbit  there  is  an  oval  or  circular  organ  composed  of 
numbers  of  parallel  and  permanent  folds,  papilla3- 
foliatce.  The  papilla3  fungiformes  of  the  rest  of  the 
tongue  also  contain  in  some  places  a  taste  goblet.  But 
most  of  the  taste  goblets  are  found  on  the  papillae  cir- 
cumvallatae  and  foliatse.  In  both  kinds  of  structures 
the  taste  goblets  are  placed  in  several  rows  close  round 
the  bottom  of  the  pit,  separating,  in  the  papillae 
circumvallatae,  the  papillae  fungiformes  from  the  fold 
of  the  mucosa  surrounding 
it  :  in  the  papillae  foliatse 
the  pits  are  represented  by 
groves  separating  the  indi- 
vidual folds  from  one 
another. 

261.  The  taste  gob- 
lets or  taste  buds  are 
barrel-shaped  structures 
(Fig.  112),  extending  in  a 
vertical  direction  through 
the  epithelium,  from  the 
free  surface  to  the  mucosa. 
Each  is  composed  of  a 
layer  of  flattened  epithelial 
cells,  elongated  in  the 
direction  of  the  goblet,  and 
forming  its  cover;  these 
are  the  tegmental  cells. 
The  interior  of  the  goblet 
is  made  up  of  a  bundle  of  spindle-shaped  or  staff- 
shaped  taste  cells.  Each  includes  an  oval  nucleus, 
and   is  drawn  out  into  an  outer  and  an  inner  fine 

N 


Fig.  112— Three  Taste  Goblets, 
highly  magnified. 

g,  The  base  of  the  goblet  next  the 
mucosa;  h,  the  free  surface;  e,  the 
epithelium  of  the  surface.     (Atlas.) 


1 94  Elements  of  Histology.     [Chap,  xxiv. 

extremity.  The  former  extends  to  the  free  surface, 
projecting  just  through  an  opening  of  the  goblet, 
and  resembles  a  fine  hair ;  the  latter  is  generally 
branched,  and  passes  towards  the  mucosa ;  there, 
probably,  it  becomes  connected  with  a  nerve-fibre,  the 
mucosa  of  these  parts  containing  rich  plexuses  of 
nerve-fibres. 

Into  the  pits  surrounded  by  taste  goblets  open  the 
ducts  of  the  serous  glands  only  (von  Ebner). 


CHAPTER   XXIY. 

THE   (ESOPHAGUS  AND   STOMACH. 

262.  I.  The  oesophagus. — Beginning  with  the 
oesophagus,  and  ending  with  the  rectum  of  the  large 
intestine,  the  wall  of  the  alimentary  canal  consists  of 
an  inner  coat  or  mucous  membrane,  an  outer  or  mus- 
cular coat,  and  outside  this  a  thin  fibrous  coat,  which, 
commencing  with  the  cardia  of  the  stomach,  is  the 
serous  covering,  or  the  visceral  peritoneum. 

The  epithelium  lining  the  inner  or  free  surface  of 
the  mucous  membrane,  of  the  oesophagus  is  a  thick, 
stratified,  pavement  epithelium, 

In  Batrachia,  not  only  the  oral  cavity  and 
pharynx,  but  also  the  oesophagus,  are  lined  with 
ciliated  columnar  epithelium. 

The  mucous  membrane  is  a  fibrous  connective 
tissue  membrane,  the  superficial  part  of  which  is 
dense — the  mucosa;  this  projects,  in  the  shape  of 
small  papilla?,  into  the  epithelium. 

The  deeper,  looser  portion  of  the  mucous  membrane 
is  the  submucosa  ;  in  it  lie  small  mucous  glands,  the 
ducts  of  which  pass  in  a  vertical  or  oblique  direction 


chap,  xxiv.]       (Esophagus  and  Stomach. 


195 


through  the  mucosa,  in  order  to  open  on  the  free  sur- 
face. In  man,  these  glands  are  relatively  scarce  ;  in 
carnivorous  animals  (dog,  cat)  they  form  an  almost 
continuous  layer  (Fig.  113). 

263.   Between    the    mucosa    and    submucosa    are 
longitudinal  bundles  of  non-striped  muscular  tissue. 

d. 


Fig.  113. — From  a  Longitudinal  Section  through  the  Mucous  Membrane 
of  the  Oesophagus  of  Dog. 

e,  The  stratified  pavement  epithelium  of  the  surface  ;  m,  the  muscularis  mucosas ; 
between  the  two  is  the  mucosa;  g,  the  mucous  glands :  d,  ducts  of  same. 
(Atlas.) 


At  the  beginning  of  the  oesophagus  they  are  absent, 
but  soon  make  their  appearance — at  first  as  small 
bundles  separated  from  one  another  by  masses  of  con- 
nective tissue ;  but  lower  down,  about  the  middle, 
they  form  a  continuous  stratum  of  longitudinal 
bundles.     This  is  the  muscularis  mucosa. 


196  Elements  of  Histology.     [Chap.  xxiv. 

Outside  the  submucosa  is  the  muscularis  externa. 
This  consists  of  a  thicker  inner  circular  and  an  outer 
thinner  longitudinal  coat.  And  outside  this  is  the  outer, 
or  limiting,  fibrous  coat  of  the  oesophagus.  In  man, 
the  outer  muscular  coat  consists  of  non-striped  muscu- 
lar tissue,  except  at  the  beginning  (about  the  upper 
third,  or  less)  of  the  oesophagus,  which  is  composed 
of  the  striped  variety ;  but  in  many  mammals  almost 
the  whole  of  the  external  muscular  coat,  except  the 
part  nearest  the  cardia,  is  made  up  of  striped  fibres. 

264.  The  large  vessels  pass  into  the  submucosa, 
whence  their  finer  branches  pass  to  the  surface  parts. 
The  superficial  part  of  the  mucosa  and  the  papilla 
contain  the  capillary  networks.  The  outer  muscular 
coat  and  the  muscularis  mucosae  have  their  own 
vascular  supply. 

There  is  a  rich  plexus  of  lymphatics  in  the  mucosa, 
and  this  leads  to  a  plexus  of  larger  vessels  in  the  sub- 
mucosa (Teichmann).  The  nerves  form  rich  plexuses 
in  the  outer  fibrous  coat ;  these  plexuses  include 
numerous  ganglia.  A  second  plexus  of  non-medullated 
fibres  lies  between  the  longitudinal  and  circular  mus- 
cular coat )  a  few  ganglia  are  connected  with  this 
plexus.  In  the  submucosa  are  also  plexuses  of  non- 
medullated  fibres.  Now  and  then  a  small  ganglion  is 
connected  also  with  this  plexus. 

265.  II.  The  stomach. — Beginning  with  the 
cardia,  the  mucous  membrane  of  the  stomach  is  covered 
with  a  single  layer  of  beautiful  thin  columnar  epithelial 
cells,  most  of  which  are  mucus-secreting  goblet  cells. 
On  the  surface  of  the  mucous  membrane  of  the  stomach 
open  numerous  fine  ducts  of  glands,  placed  very  closely 
side  by  side.  These  extend,  more  or  less  vertically,  as 
minute  tubes,  into  the  depth  of  the  mucous  membrane. 
In  the  pyloric  end,  where  the  mucous  membrane 
presents  a  pale  aspect,  the  glands  are  called  the  pyloric 
glands;  in  the  rest  of  the  stomach,  whose  mucous 


Chap.  XXIV.]  GLSOPHAGUS   AND    STOMACH.  1 97 

membrane  presents  a  reddish  or  red-brown  appear- 
ance, they  are  called  the  peptic  glands.  Owing 
to  the  very  numerous  fine  ducts  opening  on  the 
surface  of  the  mucous  membrane,  the  tissue  of  this 
latter  appears  on  a  vertical  section  to  be  made  up 
of  thinner  or  thicker  folds,  or  villi — plicae  villosae. 
But  they  are  not  real  villi. 

The  part  of  the  mucous  membrane  containing 
the  glands  is  the  mucosa  ;  outside  this  is  a  loose  con- 
nective tissue  containing  the  large  vessels — this  is 
the  submucosa.  Between  the  two,  but  belonging 
to  the  mucosa,  is  the  muscularis  mucosce,  a  thick 
stratum  of  bundles  of  non-striped  muscular  tissue, 
arranged  in  most  parts  of  the  stomach  as  an  inner 
circular  and  an  outer  longitudinal  layer.  The  tissue 
of  the  mucosa  is  dense,  owing  to  its  containing, 
placed  closely  side  by  side,  the  gland  tubes.  Be- 
tween them  is  a  delicate  connective  tissue,  in  which 
the  minute  capillary  blood-vessels  pass  in  a  direction 
vertical  to  the  surface.  Numerous  small  bundles 
of  non-striped  muscular  fibres  pass  from  the  mus- 
cularis mucosae  towards  the  surface — up  to  near  the 
epithelium  of  the  surface — forming  longitudinal  mus- 
cular sheaths,  as  it  were,  around  the  gland  tubes. 

The  plicae  villosae  of  the  superficial  part  of  the 
mucosa  contain  fibrous  connective  tissue  and  numerous 
lymphoid  cells. 

266.  The  peptic  glands  (Fig.  114)  are  more  or  less 
wavy  tubes,  extending  down  to  the  muscularis  mucosae. 
The  deep  part  is  broader  than  the  rest,  and  is  more 
or  less  curved,  seldom  branched.  This  is  the  fundus  of 
the  gland ;  near  the  surface  of  the  mucosa  is  the 
thinnest  part  of  the  tube ;  this  is  the  neck.  Two 
or  three  neighbouring  glands  join  and  open  into 
the  short  cylindrical  duct  mentioned  above.  The 
duct  is  lined  with  a  layer  of  columnar  epithe- 
lial cells,  continuous  and  identical  with  those  of  the 


198 


Elements  of  Histology.     [Chap.  xxiv. 


free  surface  of  the  mucous  membrane.  The  cavity  of 
the  duct  is  continued  as  a  very  fine  canal  into  the 
neck  and  through  the  rest  of  the  gland  tube.      Next 


Fig.  114.— Peptic  Glands. 

A,  Under  a  low  power :  d,  duct ;  n,  neck  ;  b,  part  of  the  fundus  of  a  gland 
tube  under  a  high  power ;  p,  parietal  cells ;  c,  chief  cells. 

to  the  lumen  is  a  continuous  single  layer  of  more  or 
less  transparent,  granular-looking,  epithelial  cells, 
each  with  a  reticulated  protoplasm  and  a  spherical  or 
slightly  oval   nucleus.     In  the  neck  these  cells  are 


Chap,  xxiv.]       (Esophagus  and  Stomach. 


199 


polyhedral,  but  farther  downwards  increase  to  cylin- 
drical cells,  and  in  the  fundus  of  the  gland  tube  they 
are  long  columnar.  This  layer  of  cells  bordering  the 
lumen  is  the  layer  of  chief  s 

cells  (Heidenhain.)  Outside 
them  is  the  limiting  mem- 
brana  propria  of  the  gland 
tube.  But  from  place  to 
place,  between  the  mem- 
brana  propria  and  the  chief 
cells,  are  single  oval  sphe- 
rical or  angular  large 
granular  and  opaque-look- 
ing cells,  called  the  parietal 
cells  (Heidenhain).  These 
are  more  numerous  in  the 
neck  than  in  any  other 
part  of  the  gland  ;  at  the 
fundus  they  are  few  and 
far  between,  whereas  at 
the  neck  they  form  almost 
a  continuous  layer.  Their 
protoplasm  is  densely  reti- 
culated. 

267.    The     pyloric 
glands    (Fig.   115).— The 

duct  of  each    pyloric    gland   Fig.  115.— From  a  Vertical  Section 

is  several  times  longer  than 

in  the  peptic.     The  duct  of 

the     former     occupies 

some    places    as    much    as 

half  of  the  thickness  of  the 

mucosa,  whereas  that  of  the  latter  does  not  exceed 

in  the  fundus  of  the  stomach  or  in  the  cardia,  more 

than  one-fourth  or  one-fifth  of  the  thickness. 

The  epithelium   lining    the   duct   of   the   pyloric 
glands  is  the  same  as  in  that  of  the  peptic.     Each 


mm^ssgs 


through  the  Mucous  Memhrane 
at  the  Pyloric  End  of  the 
Stomach. 

■Jy,  s,  Free  surface ;  d,  ducts  of  pyloric- 
glands  ;  n,  neck  of  same ;  m,  the  gland 
alveoli ;  mm,  muscularis  mucosce. 
(Atlas.) 


200  Elements  of  Histology.     [Chap.  xxiv. 

duct  takes  up  two  or  three  tubes  by  their  short, 
narrow,  thin  neck.  The  main  part  of  each  gland  tube 
is  convoluted  and  slightly  branched.  The  neck  is  lined 
with  a  layer  of  polyhedral  cells,  whereas  the  gland 
tube  has  a  lining  of  columnar  transparent  cells,  and 
its  lumen  is  very  conspicuous. 

During  exhaustion  these  cells  are  smaller  and  less 
transparent  than  during  secretion.  Their  protoplasm 
in  the  former  state  is  a  denser  reticulum  than  in  the 
latter,  the  transparent  interstitial  substance  in  the 
meshes  of  the  cell  reticulum  being  increased  in  amount 
during  secretion. 

The  cells  are  serous,  not  mucous,  and  the  se- 
cretion of  the  glands  cannot  therefore  be  mucous. 
According  to  Ebstein  the  secretion  is  pepsin,  and 
so  he  and  Heidenhain  consider  the  pyloric  glands 
as  simple  peptic  glands.  But  this  view  is  not  generally 
accepted. 

Between  the  mucous  membrane  with  peptic 
glands  and  the  pyloric  end  of  the  stomach  with 
pyloric  glands  there  is  a  narrow  intermediary  zone, 
in  which  the  peptic  glands  appear  by  degrees  to 
merge  into  the  pyloric  glands.  That  is,  the  short  duct 
of  the  former  gradually  elongates,  the  gland  tubes 
get  shorter  in  proportion  and  convoluted,  their 
lumen  gradually  enlarges,  and  the  parietal  cells 
become  fewer  and  ultimately  disappear. 

268.  The  mucosa  contains  isolated  lymph  follicles, 
glandulse  lenticulares,  and  in  the  pyloric  part  also 
groups  of  these — glandulse  agminatae. 

The  submucosa  is  of  very  loose  texture,  and  enables 
the  mucosa  to  become  easily  folded  in  all  directions. 

The  muscular  coat  is  very  thick,  and  consists  of 
an  outer  longitudinal  and  an  inner  thicker  circular 
stratum  of  non-striped  muscular  tissue.  Numerous 
oblique  bundles  are  found  in  the  inner  section  of  the 
circular  stratum. 


Chap,  xxv.]    Small  and  Large  Intestine.         201 

The  gland  tubes  are  ensheathed  in  a  longitudinal 
network  of  capillary  blood-vessels  derived  from  arteries 
of  the  submucosa.  This  network  forms  on  the  surface 
a  special  dense  horizontal  layer,  from  which  the  venous 
branches  are  derived.  The  outer  muscular  coat  and  the 
muscularis  mucosae  possess  their  own  vascular  supply. 

269.  The  lymphatics  form  a  network  in  the 
mucosa  near  the  fundus  of  the  glands.  Into  this 
plexus  lead  lymphatics  running  longitudinally  between 
the  glands  anastomosing  with  one  another  freely,  and 
extending  to  near  the  surface  (Loven).  Another 
plexus  belongs  to  the  submucosa. 

Between  the  longitudinal  and  circular  stratum  of 
the  outer  muscular  coat,  and  extending  parallel  to  the 
surface,  is  a  plexus  of  non-medullated  nerve-branches 
with  a  few  ganglia  in  its  nodes.  This  corresponds  to  the 
plexus  of  Auerbach  of  the  intestine,  and  is  destined 
for  the  outer  muscular  coat.  A  second  plexus  of  non- 
medullated  nerve-branches  with  ganglia  also  extending 
parallel  to  the  surface  lies  in  the  submucosa.  This  cor- 
responds to  the  plexus  o/Meissner  of  the  intestine,  and 
is  destined  for  the  muscularis  mucosae  and  the  mucosa. 

According  to  Rabe,  the  gastric  gland  tubes  in  the 
horse  are  surrounded  by  a  rich  plexus  of  nerve-fibres, 
terminating  in  peculiar  spindle-shaped  cells. 


CHAPTER    XXV. 

THE     SMALL    AND     LARGE     INTESTINE. 

270.  The  epithelium  covering  the  inner  or  free 
surface  of  the  mucous  membrane  of  the  small  and 
large  intestine  is  a  single  layer  of  columnar  cells,  their 
protoplasm  more  or  less  distinctly  longitudinally  fibril- 
lated  ;    their   free   surface   appears   covered    with   a 


202 


Elements  of  Histology.      [chap.  xxv. 


vertically  and 
finely  striated 
basilar  border. 
Many  cells  are 
goblet  cells. 
Underneath  the 
epithelium  is  a 
basement  mem- 
brane, the  sub- 
epithelial endo- 
thelium of  De- 
bove(seepar.39). 


Fig.  116. — Prom  a  Longitudinal  Section  through 
a  Villus  of  the  Small  Intestine. 

a.  The  epithelium  of  the  surface ;  6,  non-striped 
muscular  fibres.  Immediately  underneath  the 
epithelium  is  a  basement  membrane  with  oblong 
nuclei ;  the  tissue  of  the  villus  is  made  up  of  a 
reticulum  of  cells ;  in  its  meshes  are  lymph 
corpuscles. 

As  in  the  stomach,  so  also 
in  the  small  and  large  intes- 
tine, the  mucosa  is  connected 
with  the  outer  muscular  coat 
by  a  loose-textured  fibrous  sub- 
mucosal in  which  lie  the  large 
vascular  trunks,  and  in  many 
places  larger  or  smaller  groups 
of  fat  cells  and  lymph  cor- 
puscles. Between  the  mucosa 
and  submucosa,  but  belonging 
to  the  former,  is  a  layer  of 
non-striped  muscular  tissue, 
the  muscularis  mucosas.  This 
is  in  many  places  composed  of 
inner  circular  and  outer  longi- 
tudinal bundles,  but  there  are 
a  good  many  places,  especially 
in  the  small  intestine,  where 
only  a  layer  of  longitudinal 
bundles  can  be  made  out. 

The  tissue  of  the  mucosa  is 
similar  in  structure  to  adenoid  ^^9^EaSSSSS%^ 
tissue  (Fig.  116),  consisting  of  I^tlffi^i^&.SB 
a  reticular  matrix   with   flat-     ^^^^Snc^S^S 


Fig.  117. — From  a  Vertical 
Section  through  the  Mucous 
Membrane  of  the  Large 
Intestine  of  Dog. 


chap,  xxv.]    Small  and  Large  Intestine. 


203 


tened  large  nucleated  endotheloid  cells  and  numerous 
smaller  lymph  corpuscles.  The  mucosa  of  the  small 
and  large  intestine  contains  simple  gland  tubes,  the 
crypts  or  follicles  of  Lieberkiihn  (Fig.  117);  they 
are  placed  vertically  and  closely  side  by  side,  extend- 


Fig.  118. — From  a  Vertical  Section  through,  a  Fold  of  the 
Mucous  Membrane  of  the  Jejunum  of  Dog. 

c.  The  mucosa,  containing  the  crypts  of  Lieberkiihn,  and  projecting 
as  the  villi ;  m,  muscularis  mucosae ;  *,  submucosa.   (Atlas.) 


ing  from  the  free  surface,  where  they  open,  to  the 
muscularis  mucosae.  These  glands  possess  a  large 
lumen,  and  are  lined  with  a  single  layer  of  columnar 
epithelial  cells,  many  of  them  goblet  cells. 

271.  In  the  small  intestine  the  tissue  of  the 
mucosa  projects  beyond  the  general  surface  in  the 
shape  of  very  numerous  fine,  longer  or  shorter,  cylin- 
drical, conical  or  leaf-shaped  villi  (Fig.  118).  These 
are,  of  course,  covered  with  the  columnar  epithelium 


204 


Elements  of  Histology.      LChap.  xxv. 


of  the  general  surface,  and  their  tissue  is  the  same  as 
that  of  the  mucosa — i.e.,  adenoid  tissue — with  the 
addition  of :  (a)  One  or  two  central  wide  chyle  (lymph) 
vessels  (see  Fig.  120),  their  wall  being  a  single  layer 
of  endothelial  plates,  (b)  Along  these  chyle  vessels 
are  longitudinal  bundles  of  non-striped  muscular  tissue, 
extending  from  the  base  to  the  apex  of  the  villus, 
terminating  in  connection  with  the  cells  of  the  base- 
ment membrane — i.e.,  the  subepithelial  endothelium. 

(c)  A  network  of 
capillary  blood- 
vessels extending 
over  the  whole  of 
the  villus  close  to 
the  epithelium  of 
the  surface  (Fig. 
119).  This  capil- 
lary network  de- 
rives its  blood 
from  an  artery  in 
about  the  middle 
or  upper  part  of 
the  villus.  Two  ve- 
nous vessels  carry 
away  the  blood 
from  the  villus. 
The  Lieberkiihn's  crypts  open  between  the  bases  of 
the  villi. 

At  the  sides  of  the  villi  of  the  small  intestine, 
and  at  the  sides  of  the  plicae  villosae  of  the  stomach 
(see  a  former  chapter),  there  exist  amongst  the  epithe- 
lium of  the  surface  peculiar  goblet-shaped  groups  of 
epithelial  cells,  which,  as  Watney  has  shown,  are  due 
to  local  multiplication  of  the  epithelial  cells. 

272.  Lymph  follicles  occur  singly  in  the  submucosa, 
and  extend  with  their  inner  part  or  summit  through 
the  muscularis  mucosae  into  the  mucosa  to  near  the 


Fig.  119. — From  a  Vertical  Section  through 
the  Small  Intestine  of  Mouse;  the  Blood- 
vessels are  injected. 

The  networks  of  the  capillaries  of  the  villi  are 
well  shown.    (Atlas.) 


chap,  xxv.j    Small  and  Large  Intestine.        205 

internal  free  surface  of  the  latter  (Fig.  120).  These 
are  the  solitary  lymph  follicles  of  the  small  and  large 
intestine ;  in  the  latter  they  are  larger  than  in  the 
former. 

Agminated  glands,  or  Peyer's  glands,  are  larger  or 
smaller  groups  of  lymph  follicles,  more  or  less  fused 


*>,* 


Fig.  120. — Prom  a  Section  through,  a  part  of  a  Human  Peyer's  Patch, 
showing  the  distribution  of  the  Lymphatic  Vessels  in  the  Mucosa 
and  Submucosa. 

a,  Villi,  with  central  chyle  vessel ;  6,  Lieberktihn's  crypts ;  c,  region  of  muscularis 
mucosae;  /,  lymph  follicle;  g,  network  of  lymphatics  around  the  lymph 
follicle ;  l,  lymphatic  network  of  the  submucosa ;  k,  an  efferent  lymphatic 
trunk.     (Frey.) 

with  one  another,  and  situated  with  their  main  part 
in  the  submucosa,  but  extending  with  their  summit 
to  the  epithelium  of  the  free  surface  of  the  mucosa. 
In  the  lower  part  of  the  ileum  these  Peyer's  glands 
are  very  numerous.  The  epithelium  covering  the 
summits  of  these  lymph  follicles  is  invaded  by,  and 
more  or  less  replaced  by,  the  lymph  corpuscles  of  the 


206  Elements  of  Histology.      [Chap.  xxv. 

adenoid  tissue  of  the  follicles  (Watney),  similar  to 
what  is  the  case  in  the  tonsils  (see  par.  124). 

The  outer  muscular  coat  consists  of  an  inner  thicker 
circular  and  an  outer  thinner  longitudinal  stratum  of 
non-striped  muscular  tissue. 

In  the  large  intestine,  in  the  "ligamenta,"  only 
the  longitudinal  layer  is  present,  and  is  much  thickened. 

273.  The  blood-vessels  form  separate  systems  of 
capillaries  for  the  serous  covering,  for  the  outer  mus- 
cular coat,  for  the  muscularis  mucosae,  and  the  richest 
of  all  for  the  mucosa  with  its  Lieberkuhn's  crypts. 
The  capillary  network  of  the  villi  is  connected  with 
that  of  the  rest  of  the  mucosae. 

The  chyle  vessel,  or  vessels  of  the  villi,  commence 
with  a  blind  extremity  near  the  apex  of  the  villi. 
At  the  base  the  chyle  vessel  becomes  narrower,  and 
empties  itself  into  a  plexus  of  lymphatic  vessels  and 
sinuses  belonging  to  the  mucosa,  and  situated  between 
the  crypts  of  Lieberkiihn  (Fig.  120).  This  network  is 
the  same  both  in  the  small  and  large  intestine,  as 
is  also  that  of  the  lymphatics  of  the  submucosa  with 
which  the  former  communicates.  The  lymph  follicles 
are  generally  surrounded  with  sinuous  vessels  of  this 
plexus.  The  efferent  trunks  of  the  submucous  plexus, 
while  passing  through  the  outer  muscular  coat  in  order 
to  reach  the  mesentery,  take  up  the  efferent  vessels  of 
the  plexus  of  the  lymphatics  of  the  muscular  coat. 

The  chyle,  composed  of  granules  and  globules 
of  different  but  minute  sizes,  passes  from  the  inner 
free  surface  of  the  mucous  membrane  of  the  small 
intestine  through  the  epithelium  (probably  through  its 
fluid  interstitial  cement  substance)  into  the  reticulum 
of  the  villus  matrix,  and  from  thence  the  central 
chyle  vessel,  and  farther  into  the  plexus  of  vessels 
of  the  mucosa  and  submucosa. 

Owing  to  the  peripheral  disposition  of  the 
capillaries   in   the   villi,   and   owing   to   the   greater 


chap,  xxv.]    Small  and  Large  Intestine 


207 


filling  with  blood  of  the  capillaries  during  digestion, 
the  villi  are  thrown  into  a  state  of  turgescence  during 
this  period,  in  consequence  of  which  the  central  chyle 
vessels  are  kept  distended.  Absorption  is  thus 
greatly  supported.  The  contraction  of  the  muscular 
tissue  of  the  villi  and  of  the  muscular  coat  of  the  in- 


Fig.  120a. — Plexus  Myentericus  of  Auerbach  of  the  Small  Intestine 
of  a  new-born  Child. 

The  minute  circles  and  ovals  indicate  ganglion  cells.    (Atlas.) 


testine  greatly  facilitates  the  absorption  and  discharge 
of  the  chyle. 

274.  The  non-medullated  nerves  form  a  rich 
plexus,  called  the  the  plexus  myentericus  of  Auerbach 
(Fig.  120a),  with  groups  of  ganglion  cells  in  the 
nodes ;  this  plexus  lies  between  the  longitudinal  and 
circular  muscular  coat.  Another  plexus  connected 
with  the  former  lies  in  the  submucous  tissue  ;  this 
is  the  plexus  of  Meissner,  with   ganglia.      In   both 


2o8 


Elements  of  Histology.     [Chap.  xxvi. 


plexuses  the  branches  are  of  a  very  variable  thickness  \ 
they  are  groups  of  simple  axis  cylinders,  held  together 
by  a  delicate  endothelial  sheath. 


CHAPTER  XXVI. 

THE  GLANDS  OF  BRUNNER,  AND  THE  PANCREAS. 

275.   At  the  passage  of  the  pyloric  end  of  the 
stomach  into  the  duodenum  (Fig.  121),  and  in  the  first 


&■'<* 


Fig.  121. — Vertical  Section  through,  the  Mucous  Membrane  of  the 
end  of  Stomach  and  commencement  of  Duodenum. 

»,  Villi  of  duodenum  ;  b,  a  lymph  follicle ;  c,  Lieberkuhn's  crypts  :  d,  mucosa  cf 
pyloric  end  of  stomach  ;  g,  the  alveoli  of  the  pyloric  glands;  t,  the  Fame  In 
the  submucosa;  they  are  continued  into  the  duodenum  as—*,  the  Brunner'a 
glands ;  m,  the  muscularis  mucosas.    (Atlas.) 


Chap.  XXVI.] 


The  Pancreas. 


209 


or 

gland. 


part  of  the  latter,  is  a  continuous  layer  of  gland  tissue 
in  the  submucosa,  composed  of  convoluted,  more  or  less 
branched  tubes  grouped  into  lobules,  and  permeated 
by  bundles  of  non-striped  muscular  tissue,  outrunners 
of  the  muscularis  mucosae.  These  are  the  glands  of 
Brunner.  Numerous  thin  ducts  lined  with  a  single 
layer  of  columnar  epithelial  cells  pass  through  the 
mucosa,  and  open  into  the  crypts  of  Lieberkiihn  be- 
tween the  bases  of  the  villi.  The  gland  tubes  of 
Brunner's  glands  are  identical  in  structure  with  the 
pyloric  glands,  with  which  they  form  a  direct  ana- 
tomical continuity. 

276.  The  pancreas  (Fig.  122)  is  in  most  respects 
identical  in  struc- 
ture with  a  serous 
true  salivary 
The  connec- 
tive tissue  frame- 
work, the  distribu- 
tion of  the  blood- 
vessels and  lym- 
phatics, and  of  the 
gland  tissue  in  lobes 
and  lobules,  with  the 
corresponding  inter- 
and  intra  -  lobular 
ducts,  is  similar  in 
both  cases.  The 
epithelium  lining 
the    latter   ducts  is 

Only  faintly  Striated,  Fig.  122.— From    a    Section    through    the 

not    by    any    means  Pancreas  of  Dog. 

!•    ,.       ,-,                  .  a,  The  alveoli  (tubes)  of  the  gland;  the  lining 

SO    distinctly     as     m  eel  Is  show  an  outer  homogeneous  and  an  inner 

xi              1  •                 ,     n  granular-looking  portion  :   d,  a  minute  duct. 

the   salivary   tubes.      (Atias.) 
The  alveoli  or  acini 

are  club-shaped,  flask-shaped,  shorter  or  longer  cylin- 
drical, and  convoluted. 


210  Elements  of  Histology.   [Chap,  xxvil 

277.  The  intermediary  part  of  the  duct  and  its 
passage  into  the  alveoli  is  the  same  as  in  the 
salivary  glands.  The  cells  lining  the  alveoli  are 
columnar  or  pyramidal,  and  show  an  outer  homo- 
geneous, or  faintly  and  longitudinally  striated  zone 
(Langerhans,  Heidenhain),  and  an  inner  more  tran- 
sparent granular-looking  zone.  The  nucleus  of  the 
cell  is  spherical,  and  lies  in  about  the  middle.  According 
to  the  state  of  secretion  the  two  zones  vary  in  amount, 
one  at  the  expense  of  the  other. 

The  lumen  of  the  alveoli  is  very  minute,  and 
in  the  beginning  of  the  alveoli,  i.e.,  next  to  the 
intermediary  part  of  the  duct,  are  seen  spindle-shaped 
cells  occupying  the  lumen,  the  centroacinous  cells  of 
Langerhans. 

In  the  rabbit's  pancreas  Kiihne  and  Lea  have 
shown  that  there  are  peculiar  accumulations  of  cells 
between  the  alveoli,  which  are  supplied  with -veritable 
glomeruli  of  capillary  blood-vessels. 


CHAPTER    XXVIL 

THE    LIVER. 

278.  The  outer  surface  of  the  liver  is  covered  with 
a  delicate  serous  membrane,  the  peritoneum,  which, 
like  that  of  other  abdominal  organs,  has  on  its  free 
surface  a  layer  of  endothelium.  It  consists  chiefly  of 
fibrous  connective  tissue. 

At  the  hilum  or  porta  hepatis  this  connective 
tissue  is  continued  into  the  interior,  and  becomes  one 
with  the  connective  tissue  of  the  Glisson's  capsule,  or 
the  interlobular  connective  tissue  (connective  tissue 
of  the  portal   canals).      This  tissue   is   fibrous,  and 


Chap.  XXVI 1.] 


The  Liver. 


211 


more  or  less  lamellated ;  by  it  the  substance  of 
the  liver  is  subdivided  into  numerous,  more  or  less 
polyhedral,  solid  lobules  or  acini  (Fig.  123),  each  about 
-x-th  of  an  inch  in  diameter.  According  to  whether 
the  interlobular 
tissue  forms  com- 
plete boundaries 
or  not,  the  acini 
appear  well  de- 
fined from  one 
another  (pig,  ice- 
bear),  or  more  or 
less  fused  (man 
and  carnivorous 
animals  and  ro- 
dents). 

Within  each 
acinus  there  is 
only  very  scanty 
connective  tissue, 
in  the  shape  of 
extremely  delicate 

Tvnnrlle»c    anrl    flaf  s,  Interlobular    connective    tissue,   containing  the 

uujiuj.t&    dim    liau-  interlobular  blood-vessels,  i.e.,  the  branches  of  the 

+o-norl     prmiiPftivo.  hepatic  artery  and  portal  vein,  and  the  interlobular 

teiieu    cuiinc^uiv  e  ^jjg  ducts .  if  intralobular  or  central  vein.   (Atlas.) 

tissue  cells.    Occa- 
sionally,   especially    in    the    young   liver,    migratory 
cells  are  to  be  met  with  in  the  acini  and  in  the  tissue 
between  them. 

279.  The  vena  portse  having  entered  the  hilum 
gives  off  rapidly  numerous  branches,  which  follow  the 
interlobular  tissue  in  which  they  are  situated,  and 
they  form  rich  plexuses  around  each  acinus  ;  these  are 
the  interlobular  veins  (Fig.  124).  Numerous  capillary 
blood-vessels  are  derived  from  these  veins.  These 
capillaries  pass  in  a  radiating  direction  to  the  centre 
of  the  acinus,  at  the  same  time  anastomosing  with 
one  another  by  numerous  transverse  branches.    In  the 


Fig.  123. — From  a  Section  through  the  Liver 
of  Pig.  Five  lobules  are  shown.  They  are 
well  separated  from  one  another  by  the 
interlobular  tissue. 


2i2  Elements  of  Histology.   [Chap. xxvii. 

centre  of  the  acinus  the  capillaries  become  con- 
fluent into  one  large  vein,  the  central  or  intralobular 
vein  The  intralobular  veins  of  several  neighbouring 
acini  join  so  as  to  form  the  sublobular  veins,  and 
these   lead   into  the  efferent  veins  of    the  liver,   or 


Fig.  124. — From  a  Vertical  Section  through  the  Liver  of  Eabbit ;  the 
Blood-vessels  and  Bile-vessels  injected. 

a,  Interlobular  veins  surrounded  by  interlobular  bile-ducts ;  these  latter  take  up 
the  network  of  fine  intralobular  bile  capillaries;  the  meshes  of  this  net- 
work correspond  to  the  liver  cells;  6,  the  intralobular  or  central  A-ein. 
(Atlas.) 

the  hepatic  veins,  which  finally   pass   into  the   vena 
cava  inferior. 

280.  The  substance  of  each  acinus — i.e.,  the 
tissue  between  the  capillary  blood-vessels — is  com- 
posed of  uniform  polygonal  protoplasmic  epithelial 
cells,  of  about  j^th  of  an  inch  in  diameter ;  these 
are  the  liver  cells.  Owing  to  the  peculiar,  more  or 
less  radiating,  arrangement  of  the  capillaries,  the  liver 
cells  appear  to  form  columns  or  cylinders,  also  more 
or   less    radiating  from   the   periphery   towards   the 


Chap.  XXVII.] 


The  Liver. 


213 


centre  of  the  acinus.     Sometimes  the  liver  cells  contain 
minute  pigment  granules. 

Each  liver  cell  shows  a  more  or  less  fibrillated  and 
reticulated  protoplasm  (Kupfer),  and  in  the  centre  a 
spherical  nucleus  with  its  reticulum,   generally  with 
one  or  more  nucleoli. 
During  activity  the 
liver  cells  are  larger 


o^-*-        ?== 


and  look  more  gran- 
ular than  after 
action. 

The  liver  cells 
are  joined  with  one 
another  by  an  albu- 
minous cement  sub- 
stance, in  which  are 
left  fine  channels ; 
these  are  the  bile 
capillaries,  or  intra- 
lobular bile  vessels 
(Fig.  125).  In  a 
successfully  injected 
preparation,  the 
liver     cells    appear 

separated  everywhere  from  one  another  by  a  bile 
capillary,  and  these  form  for  the  whole  acinus  a  con- 
tinuous intercommunicating  network  of  minute 
channels.  Where  the  liver  cells  are  in  contact  with 
a  capillary  blood-vessel,  there,  of  course,  are  no  bile 
capillaries,  since  these  exist  only  between  liver  cells. 

281.  At  the  margin  of  the  acinus  the  bile  capil- 
laries are  connected  with  the  lumen  of  minute  tubes ; 
these  possess  a  membrana  propria  and  a  lumen  lined 
with  a  single  layer  of  transparent  polyhedral  epithelial 
cells.  These  are  the  small  interlobular  bile  ducts 
(Fig.  124).  Their  epithelial  cells  are  in  reality  con- 
tinuous with  the  liver  cells.     They  join  so  as  to  form 


Fig.  125. — From  a  Lobule  of  the  Liver  of 
Babbit,  in  which  Blood  and  Bile  Vessels 
had  been  injected,  more  highly  magnified 
than  in  Fig.  124. 

b,  Bile  capillaries  between  the  liver  cells  ;  these 
are  well  shown  as  nucleated  polygonal  cells, 
each  with  a  distinct  reticulum;  c,  capillary 
blood-vessels.    (Atlas.) 


214  Elements  of  Histology.   [Chap,  xxvii. 

the  larger  interlobular  bile  ducts,  lined  with  more  or  less 
columnar  epithelium.  The  first  part  of  the  bile  duct 
lined  with  polyhedral  cells  corresponds  to  the  inter- 
mediary part  of  the  ducts  of  the  salivary  glands. 
The  interlobular  bile  ducts  form  networks  in  the  inter- 
lobular tissue.  Towards  the  hilum  they  become  of 
great  diameter,  and  their  wall  is  made  up  of  fibrous 
tissue,  with  non-striped  muscular  tissue.  Small 
mucus-secreting  glands  are  in  their  wall,  and  open 
into  their  lumen. 

The  wall  of  the  hepatic  duct,  and  of  the  gall 
bladder,  are  merely  exaggerations  of  this  structure. 

282.  The  hepatic  artery  follows  in  its  ramification 
the  interlobular  veins.  The  arterial  branches  form 
plexuses  in  the  interlobular  tissue,  and  they  supply 
the  capillary  blood-vessels  of  the  interlobular  con- 
nective tissue,  and  especially  of  the  bile  ducts.  The 
capillary  blood-vessels  of  the  bile  ducts  join  so  as 
to  form  small  veins  which  finally  empty  themselves 
into  the  interlobular  veins.  The  anastomoses  of  the 
capillary  blood-vessels,  derived  from  the  arterial 
branches,  directly  with  the  capillary  blood-vessels  of 
the  acini,  are  insignificant  (Cohnheim  and  Litten). 
The  serous  covering  of  the  liver  contains  special 
arterial  branches — rami  capsulares.  Networks  of  lym- 
phatics— deep  lymphatics — are  present  in  the  inter- 
lobular connective  tissue,  forming  plexuses  around 
the  interlobular  blood-vessels  and  bile  ducts,  and 
occasionally  forming  a  perivascular  lymphatic  around 
a  branch  of  the  hepatic  vein.  Within  the  acinus, 
the  lymphatics  are  represented  only  by  spaces  and 
clefts  existing  between  the  liver  cells  and  capillary 
blood-vessels ;  these  are  the  intralobular  lymphatics 
(Macgillivry,  Frey,  and  others).  They  anastomose 
at  the  margin  of  the  acinus  with  the  interlobular 
lymphatics. 

In  the  capsule  of  the  liver  is  a  special  network 


Chap. xxviii.]   Organs  of  Respiration:  215 

of  lymphatics,  called  the  superficial  lymphatics. 
Numerous  branches  pass  between  this  network  and 
those  of  the  interlobular  lymphatics. 


CHAPTER   XXVIII. 

THE    ORGANS    OF    RESPIRATION. 

283.  I.  The  larynx. — The  supporting  frame- 
work of  the  larynx  is  formed  by  cartilage.  In  the 
epiglottis  the  cartilage  is  elastic  and  reticulated, 
i.e.,  the  cartilage  plate  is  perforated  by  numerous 
smaller  and  larger  holes.  The  cartilages  of  Santorini 
and  Wrisbergii,  the  former  attached  to  the  top  of 
the  arytenoid  cartilage,  the  latter  enclosed  in  the 
aryteno-epiglottidean  fold,  are  also  elastic.  The 
thyroid,  cricoid,  and  arytenoid  cartilages  are  hyaline. 
All  these  are  covered  with  the  usual  perichondrium. 

A  small  nodule  of  elastic  cartilage  is  enclosed  in 
the  front  part  of  the  true  vocal  cord.  This  is  the 
cartilage  of  Luschka. 

The  mucous  membrane  lining  the  cavity  of  the 
larynx  (Fig.  126)  has  the  following  structure  : — 

The  epithelium  covering  the  free  surface  is 
stratified  columnar  ciliated,  i.e.,  the  most  superficial 
layer  is  made  up  of  conical  cells  with  cilia  on  their 
surface  ;  then  between  the  extremities  of  these  cells 
are  wedged  in  spindle-shaped  and  inverted  conical  cells. 
Numerous  goblet  cells  are  found  amongst  the  superficial 
cells.  The  two  surfaces  of  the  epiglottis  and  the 
true  vocal  cord  are  covered  with  stratified  pavement 
epithelium. 

Underneath  the  epithelium  is  a  basement  mem- 
brane separating  the  former  from  the  mucous  mem- 
brane proper. 


2l6 


Elements  of  Histology.  [Chap.xxvm. 


284.  The  mucous  membrane  is  delicate  connective 
tissue  with  numerous  lymph  corpuscles.  In  the  pos- 
terior surface  of  the  epiglottis,  in  the  false  vocal  cord, 


-a 


Fig.  126. — From  a  Longitudinal  Section  through  the  Ventricle 
of  the  Larynx  of  a  Child. 

a,  True  vocal  cord  ;  6,  false  vocal  cord ;  c,  a  nodule  of  elastic  cartilage  (cartilage 
of  Luscbka);  d,  ventricle;  I,  lymphatic  tissue  ;  m,  bundles  of  the  thyro- 
arytenoid muscle  in  transverse  section.    (Atlas.) 

and  in  the  lower  parts  of  the  larynx,  but  especially  in 
the  ventricle,  this  infiltration  amounts  to  diffuse 
adenoid  tissue,  and  even  to  the  localisation  of  this 
as  lymph  follicles.  In  both  surfaces  of  the  epiglottis, 
and  in  the  true  vocal  cords,  the  mucosa  extends  into 
the  stratified  pavement  epithelium  in  the  shape  of 
minute  papillae. 


chap.xxvin.]  Organs  of  Respiration.  217 

In  the  lower  part  of  the  larynx  the  mucous  mem- 
brane contains  bundles  of  elastic  fibres  connected  into 
networks,  and  running  in  a  longitudinal  direction 
These  elastic  fibres  are  found  chiefly  in  the  superficial 
parts  of  the  mucous  membrane.  In  the  true  vocal 
cord  the  mucosa  is  entirely  made  up  of  elastic  fibres 
extending  in  the  direction  of  the  vocal  cord. 

285.  The  deeper  part  of  the  mucous  membrane  is 
of  loose  texture,  and  corresponds  to  the  sub-mucosa ; 
in  it  are  embedded  numerous  mucous  glands,  the  ducts 
of  which  pass  through  the  mucosa  and  open  on  the 
free  surface.  The  alveoli  of  the  glands  are  of  the 
nature  of  mucous  alveoli,  i.e.,  a  considerable  lumen 
lined  with  a  layer  of  mucous  goblet  cells.  There  are, 
however,  also  alveoli  lined  with  columnar  albuminous 
cells,  and  such  as  have  both  side  by  side,  as  in  the 
case  of  the  sub-lingual  gland  of  the  dog.  The  ciliated 
epithelium  of  the  surface  in  some  places  extends  also 
for  a  short  distance  into  the  duct.  The  true  ocal 
cords  have  no  mucous  glands. 

The  blood-vessels  terminate  as  the  capillary  net- 
work in  the  superficial — i.e.,  sub-epithelial — layer  of  the 
mucosa;  where  there  are  papillse — i.e.,  in  the  epiglottis 
and  true  vocal  cord — these  receive  a  loop  of  capillary 
blood-vessels.  The  lymphatics  form  superficial  networks 
of  fine  vessels,  and  deep  submucous  networks  of  large 
vessels.  These  are  of  enormous  width  and  size  in  the 
membrane  of  the  anterior  surface  of  the  epiglottis. 
The  finer  nerves  form  superficial  plexuses  of  non- 
medullated  fibres.  Here,  according  to  Luschka  and 
Boldyrew,  there  are  end  bulbs.  Taste-buds  have 
been  found  in  the  posterior  surface  of  the  epiglottis 
(Verson,  Schofield,  Davis),  and  also  in  the  deeper 
parts  of  the  larynx  (Davis). 

286.  II.  The  trachea. — The  trachea  is  very 
similar  in  structure  to  the  lower  part  of  the  larynx, 
from  which  it  differs   merely  in  possessing  the  rings 


2l8 


Elements  of  Histology.  [Chap.xxvm. 


of  hyaline  cartilage,  and  in  possessing,  in  the  posterior 
or    membranous    portion,    circular     bundles    of    non- 


Fig.  127. — From  a  Longitudinal  Section  through  the  Trachea  of  a  Child. 

a,  The  stratified  columnar  ciliated  epithelium  of  the  internal  free  surface ;  6, 
the  basement  membrane;  c,  the  mucosa;  d,  the  networks  of  longitudinal 
elastic  fibres ;  the  oval  nuclei  between  them  indicate  connective  tissue 
corpuscles;  e,  the  submucous  tissue  containing  mucous  glands;/,  large 
blood-vessels;  g,  fat  cells;  h,  hyaline  cartilage  of  the  tracheal  rings. 
(Atlas.) 

striped  muscular  tissue,  extending,  as  it  were,  between 
the  ends  of  the  rings.  Its  component  parts  are  (Fig. 
127)  ;— 

(a)  A  stratified  columnar  ciliated  epithelium. 

(b)  A  basement  membrane. 


chap. xxviii.]   Organs  of  Respiration.  219 

(c)  A  mucosa,  with  the  terminal  networks  of 
capillary  blood-vessels,  and  infiltrated  with  adenoid 
tissue. 

(d)  A  layer  of  longitudinal  elastic  fibres. 

(e)  A  loosely-textured  submucous  tissue,  contain- 
ing the  large  vessels  and  nerves  and  small  mucous 
glands.  Occasionally  the  gland  or  its  duct  is  embedded 
in  a  lymph  follicle. 

287.  III.  The  bronchi  and  the  lung*. — 
The  bronchi  branch  within  the  lung  dendritically 
into  finer  and  finer  tubes.  The  finest  branches 
are  the  terminal  bronchi.  In  the  bronchi  we  find, 
instead  of  rings  of  hyaline  cartilage,  as  in  the  trachea, 
larger  and  smaller  oblong  or  irregularly-shaped  plates 
of  hyaline  cartilage  distributed  more  or  less  uniformly 
in  the  circumference  of  the  wall.  Towards  the  small 
microscopic  bronchi,  these  cartilage  plates  gradually 
diminish  in  size  and  number.  The  epithelium,  the 
basement  membrane,  the  sub-epithelial  mucosa,  and 
the  layer  of  longitudinal  elastic  fibres,  remain  the  same 
as  in  the  trachea.  The  submucous  tissue  contains 
small  mucous  glands. 

288.  Between  the  sub-epithelial  mucosa  and  sub- 
mucosa  is  a  continuous  layer  of  circular  non-striped 
muscular  tissue.  In  the  smaller  microscopic  bronchi 
this  layer  is  one  of  the  most  conspicuous.  By  the 
contraction  of  the  circular  muscular  coat  the  mucosa 
is  placed  in  longitudinal  folds. 

The  state  of  contraction  and  distension  of  the 
small  bronchi  bears  an  important  relation  to  the  aspect 
of  the  epithelium,  which  appears  as  a  single  layer  of 
columnar  cells  in  the  distended  bronchiole,  and  strati- 
fied when  the  bronchiole  is  contracted. 

The  distribution  of  the  blood-vessels  is  the  same 
as  in  the  trachea.  Lymph  follicles  are  met  with  in 
the  submucous  tissue  of  the  bronchial  wall  in  animals 
and  man. 


220  Elements  of  Histology.  [Chap. xxviii. 

The  lymphatic  networks  of  the  bronchial  mucous 
membrane  are  very  conspicuous.  Those  of  the  sub- 
mucous tissue,  i.e.,  the  peribronchial  lymphatics,  anas- 
tomose with  those  surrounding  the  pulmonary  blood- 
vessels. 

Pigment  and  small  particles  can  be  easily  absorbed 
through  the  cement  substance  of  the  epithelium 
into  the  radicles  of .  the  superficial  lymphatics,  whence 
they  pass  readily  into  the  (larger)  peribronchial  lym- 
phatics. 

In  connection  with  the  nerve  branches  in  the 
bronchial  wall  are  minute  ganglia. 

289.  Each  terminal  bronchiole  branches  into 
several  wider  tubes  called  the  alveolar  ducts,  or  infundi- 
bula  ;  each  of  these  branches  again  into  several  similar 
ducts.  All  ducts,  or  infundibula,  are  closely  beset  in 
their  whole  extent  with  spherical,  or,  being  pressed 
against  one  another,  with  polygonal,  vesicles— the  air- 
cells  or  alveoli — opening  by  a  wide  aperture  into  the 
alveolar  duct  or  infundibulum,but  not  communicating 
with  each  other.  The  infundibula  are  much  wider 
than  the  terminal  bronchioles,  and  also  wider  than 
the  alveoli. 

290.  All  infundibula  with  their  air-cells,  belonging 
to  one  terminal  bronchiole,  represent  a  conical  struc- 
ture, the  apex  of  which  is  formed  by  the  terminal 
bronchus.  Such  a  conical  mass  is  a  lobule  of  the  lung, 
and  the  whole  tissue  of  the  lung  is  made  up  of  such 
lobules  closely  aggregated,  and  arranged  as  lobes. 
The  lobules  are  separated  from  one  another  by  delicate 
fibrous  connective  tissue ;  this  forms  a  continuity 
with  the  connective  tissue  accompanying  the  bron- 
chial tubes  and  large  vascular  trunks,  and  with  these 
is  traceable  to  the  hilum.  On  the  other  hand,  the 
interlobular  connective  tissue  of  the  superficial  parts 
of  the  lung  is  continuous  with  the  fibrous  tissue 
of  the  surface  called  the  pleura  pulmonalis.      This 


chap. xxviii.]   Organs  of  Respiration: 


221 


membrane  contains  numerous  elastic  fibres,  and 
on  the  free  surface  is  covered  with  a  layer  of  endo- 
thelium. 

In  some  instances  (guinea-pig)  the  pleura  pulmo- 
nalis  contains  bundles  of  non-striped  muscular  tissue. 


F'g.  128.— From  a  Section  through  the  Lung  of  Cat,  stained  with  Nitrate 

of  Silver. 

a,  An  infundibuluni  or  alveolar  duct  in  cross  section ;  5,  groups  of  polyhedral 
cells  lining  one  part  of  the  inf  undibulum,  the  rest  being  lined  with  flattened 
transparent  epithelial  scales ;  c,  the  alveoli  lined  with  flattened  epithelial 
scales ;  here  and  there  between  them  is  seen  a  polyhedral  granular  epithelial 
cell.    (Atlas.) 


The  lobes  of  the  lung  are  separated  from  one 
another  by  large  septa  of  connective  tissue — the  liga- 
menta  pulmonis. 

291.  The  terminal  bronchi  contain  no  cartilage 


222  Elements  of  Histology.  [Chap. xxviii. 

or  mucous  glands  in  their  wall.  This  is  made  up  of 
three  coats  :  (a)  a  tiny  epithelium — a  single  layer  of 
small  polyhedral  granular-looking  cells  ;  (6)  a  circular 
muscular  coat  of  non-striped  muscular  tissue;  and 
(c)  a  fine  adventitia  of  elastic  fibres,  arranged  chiefly 
as  longitudinal  networks. 

292.  Tracing  the  elements  constituting  the  wall 
of  a  terminal  bronchiole  into  the  infundibula  and  air- 
cells  (Fig.  128),  we  find  the  following  changes  :  (a)  the 
polyhedral  granular-looking  epithelial  cells  forming  a 
continuous  lining  in  the  terminal  bronchiole,  are  trace- 
able into  the  infundibulum  only  as  larger  or  smaller 
groups ;  between  these  groups  of  small  polyhedral 
granular-looking  cells  large,  flat,  transparent,  homo- 
geneous, nucleated,  epithelial  scales  make  their  ap- 
pearance. The  farther  away  from  the  terminal 
bronchiole,  the  fewer  are  the  groups  of  polyhedral 
granular-looking  cells.  In  all  infundibula,  however, 
the  transparent  scales  form  the  chief  lining.  This 
becomes  still  more  marked  in  the  air-cells.  There 
the  small  polyhedral  granular-looking  cells  are  trace- 
able only  singly,  or  in  groups  of  two  or  three  (Elens), 
the  rest  of  the  cavity  of  the  air-cells  being  lined  with 
the  large  transparent  scales. 

In  the  foetal  state  all  cells  lining  the  infundibula 
and  air-cells  are  of  the  small  polyhedral  granular- 
looking  variety  (Kiittner).  With  the  expansion  of 
the  lungs  during  the  first  inspiration  many  of  these 
cells  change  into  the  large  transparent  scales,  in  order 
to  make  up  for  the  increment  of  surface.  A  lung 
expanded  ad  maximum  shows  much  fewer  or  none  of 
the  small  polyhedral  cells ;  while  a  lung  that  is  col- 
lapsed shows  them  in  groups  in  the  infundibula, 
and  isolated  or  in  twos  or  threes  in  the  alveoli. 

293.  (b)  The  circular  coat  of  non-striped  muscular 
tissue  of  the  terminal  bronchiole  is  continued  as  a  con- 
tinuous circular    coat — but  slightly  thinner — on  the 


chap. xxviii.]   Organs  of  Respiration. 


223 


forming 


alveolar  ducts  or  infundibula,  in  their  whole  extent, 
but  not  beyond  them,  i.e.,  not  on  the  air-cells. 

(c)  The  adventitia  of  elastic  networks  is  con- 
tinued on  the  infundibula,  and  thence  on  the  air- 
cells,  where  they  form  an  essential  part  of  the  wall 
of  the  alveoli,  being  its  framework.  . 

Amongst  the    network   of    elastic   fibres 
the  wall  of  the  alveoli  is  a  network  of  branched  con 
nective  tissue  cells,   contained  as   usual  in  similarly 
shaped  branched  lacunae,   which   are  the    radicles   of 
the  lymphatic  vessels. 

294.  The  blood-vessels  and  lymphatics.— 
The  branches  of  the  pulmonary  artery  and  veins 
are  contained  within  the  connective  tissue  separat- 
ing the  lobes  and  lobules,  whence  they  can  be 
traced  into 
their  finer 
ramifications 
towards  the  in- 
fundibula and 
air-cells.  Each 
of  these  latter 
is  surrounded 
by  a  sort  of 
basket  -  shaped 
dense  network 
of  capillary 
blood  -  vessels 
(Fig.  129).  The 
capillary  net- 
works of  adja- 
cent alveoli  are 
continuous 
with  one  another,  and  stand  in  communication  on  the 
one  hand  with  a  branch  of  the  pulmonary  artery,  and 
on  the  other  with  branches  of  the  pulmonary  vein. 
The  branches  of  the  bronchial  artery  belong  to  the 


Fig;  129.— Networks  of  Capillary  Blood-vessels 
surrounding  the  Alveoli  of  the  Human  Luns?. 
(Kolliker.) 


224  Elements  of  Histology.  [Chap.xxvin. 

bronchial  walls,  which  are  supplied  by  them  with 
capillary  networks. 

The  lacunae  and  canaliculi  in  the  wall  of  the  alveoli, 
mentioned  above,  are  the  rootlets  of  lymphatic  vessels, 
which  accompany  the  pulmonary  vessels,  and  form  a 
network  around  them ;  these  are  the  deep  lymphatics, 
or  the  -perivascular  lymphatics.  They  are  connected 
also  with  the  networks  of  lymphatics  surrounding  the 
bronchi,  i.e.,  the  peribronchial  lymphatics.  The  root- 
lets of  the  superficial  air-cells  empty  themselves  into 
the  sub-pleural  plexus  of  lymphatics,  a  rich  plexus  of 
large  lymphatics  with  valves.  All  these  lymphatics 
lead  by  large  trunks  into  the  bronchial  lymph  glands. 

295.  Between  the  flattened  transparent  epithelial 
cells  lining  the  alveoli  are  minute  openings,  stomata 
(Fig.  128),  leading  from  the  cavity  of  the  air-cells  into 
the  lymph  lacuna?  of  the  alveolar  wall.  These  stomata 
are  more  distinct  during  expansion,  i.e.,  inspiration, 
than  in  the  collapsed  state.  Inspiration,  by  its  ex- 
panding the  lungs,  and  consequently  also  the  lym- 
phatics, favours  greatly  absorption.  Through  these 
stomata,  and  also  through  the  interstitial  cement 
substance  of  the  lining  epithelium,  formed  particles 
— such  as  soot  particles  of  a  smoky  atmosphere, 
pigment  artificially  inhaled,  cellular  elements,  such 
as  mucus  or  pus  corpuscles,  that  have  been  car- 
ried into  the  alveoli  from  the  bronchi  by  natural 
inspiration,  germ-particles,  &c,  find  their  way  into 
the  radicles  of  the  lymphatics ;  thence  into  the  peri- 
vascular and  sub-pleural  lymphatics,  and  finally  into 
the  bronchial  glands. 


Chap.  XXIX. J 


225 


CHAPTER   XXIX. 

THE    SPLEEN. 

296.    The  capsule  enveloping  the  spleen  is  a 
serous  membrane — the  peritoneum.     It  is  a  connective 


Fig.  130.— From  a  Vertical  Section  through  the  Spleen  of  Ape. 

a,  The  capsule  ;  b,  the  trahc-culje ;  c,  Malpighian  corpuscle  ;  d,  artery  ensheathed 
in  a  Malpighian  corpuscle  ;  e,  pulp  tissue.  (Atlas.) 

tissue  membrane  with  networks  of  elastic  fibres,  and 
covered  on  its  free  surface  with  an  endothelium.     The 
P 


226 


Elements  op  Histology,     [chap.  xxix. 


deep  part  of  the  capsule  contains  bundles  of  non-striped 
muscular  tissue  forming  plexuses.  In  man  the  bundles 
are  relatively  thin,  but  in  some  mammals — e.g., 
dog,  pig,  horse — they  are  continuous  masses  arranged 
sometimes  as  a  deep  longitudinal  and  a  superficial 
circular  layer. 

In  connection  with  the  capsule  are  the  trabecules 
(Fig.  130).  These  are  microscopical,  thicker  or  thinner 
cylindrical  bands  branching  and  anastomosing,  and 
thus  making  a  framework  in  which  the  tissue  of 
the  spleen  is  contained.  Towards  the  hilum  the 
trabecule  are  larger,  and  they  form  there  a  continuity 
with  the  connective  tissue  of  the  hilum.  They  are 
the  carriers  of  the  large  vascular  branches.  The 
trabecule  in  the  human  spleen  consist  chiefly  of 
fibrous  tissue  with  an  admixture  of  longitudinal  non- 
striped  muscular 
tissue.  This  is 
more  pronounced 
in  the  dog,  horse, 
pig,  guinea-pig,  in 
which  the  trabe- 
cule are  chiefly 
composed  of  non- 
striped  muscular 
tissue.  Following 
a  small  trabecula 
after  it  is  given 
off  from  a  larger 
one,  we  find  it 
branching  into 

still  smaller  ones, 
which  ultimately  lose  themselves  amongst  the  elements 
of  that  part  of  the  spleen  tissue  called  spleen  pulp 
(Fig.  131). 

The  meshes  of  the  network  of  the  trabecule  are 
filled  up  with  the  parenchyma.      1?his  consists  of  two 


Fig.  131.— From    a   Section    through,  the 
Pulp  of  tbe  Spleen  of  the  Pig. 

a,  Last  outrunners  of  the  muscular  trabecular ; 
b,  the  flattened  cells  forming  the  honeycombed 
matrix  of  the  pulp:  in  the  meshes  of  this 
matrix  ai-e  contained  lymphoid  cells  of  various 
sizes.    (Atlas.) 


Chap,  xxix.]  The  Spleen.  227 

kinds  of  tissues  :   (a)  the  Malpighian  corpuscles ;  and 
(6)  the  pulp  tissue. 

297.  The  Malpighian  corpuscles  are  masses 
of  adenoid  tissue  connected  with  the  branches  of  the 
splenic  artery.  Following  the  chief  arterial  trunks  as 
they  pass  in  the  big  trabecule  towards  the  interior 
of  the  spleen,  they  are  seen  to  give  off  numerous 
smaller  branches  to  the  spleen  parenchyma ;  these  are 
ensheathed  in  masses  of  adenoid  tissue  which  are 
either  cylindrical  or  irregularly-shaped,  and  in  some 
places  form  oval  or  spherical  enlargements.  These 
sheaths  of  adenoid  tissue  are  traceable  to  the  end  of 
an  arterial  branch ;  and  in  the  whole  extent  the 
adenoid  tissue  or  Malpighian  corpuscle  is  supplied  by 
its  artery  with  a  network  of  capillary  blood-vessels. 

298.  The  rest  of  the  spleen  parenchyma  is  made  up 
of  the  pulp.  The  matrix  of  this  is  a  honeycombed, 
spongy  network  of  fibres  and  septa,  which  are  the 
processes  and  bodies  of  large,  flattened,  endotheloid 
cells,  each  with  an  oval  nucleus.  In  some,  especially 
young,  animals,  some  of  these  cells  are  huge  and 
multinucleated.  The  spaces  of  the  honeycombed  tissue 
are  of  different  diameters,  some  not  larger  than  a  blood 
corpuscle,  others  large  enough  to  hold  several.  All 
spaces  form  an  intercommunicating  system.  The 
spaces  contain  nucleated  lymph  corpuscles,  more  or 
less  connected  with  and  derived  from  the  cell  plates 
of  the  matrix.  But  they  do  not  fill  the  spaces,  so 
that  some  room  is  left,  large  enough  to  allow  blood 
corpuscles  to  pass. 

The  spaces  of  the  honeycombed  pulp  matrix  are  in 
communication,  on  the  one  hand,  with  the  ends  of  the 
capillary  blood-vessels  of  the  Malpighian  corpuscles, 
and,  on  the  other,  they  open  into  the  venous  radicles 
or  sinuses  (Fig.  132),  which  are  oblong  spaces  lined 
with  a  layer  of  more  or  less  polyhedral  endothelial  cells. 
These  sinuses  form  networks,  and  lead  into  the  large 


228 


Elements  of  Histology.    [Chap.  xxix. 


venous  branches  passing  in  the  big  trabecule  to  the 
hilum.     The  venous  sinuses  in  man  and  ape  possess  a 
special  adventitia  formed  of  circular  elastic  fibrils. 
Not    all    arterial    branches     are    ensheathed    in 


Tig.  132. — From  a  Section  through  the  Spleen  of  a  Guinea-pig ;  the 
Blood-vessels  had  been  injected  (not  shown  in  the  figure). 

a,  Artery  of  Malpighian  corpuscle  ;  6,  pulp  ;  between  its  cells  are  the  minute 
blood-channels  opening  into  c,  the  radicles  of  the  veins.    (Atlas.) 


Malpighian  corpuscles  ;  some  few  fine  arterial  branches 
open  directly  into  the  spaces  of  the  pulp  matrix,  being 
invested  in  a  peculiar  reticular  or  concentrically  ar- 
ranged cellular  tissue  (not  adenoid).  These  are  the 
capillary  sheaths  of  Schweigger  Seidel. 

299.  The    blood    passes    then   from    the   arterial 
branches  through  the  capillaries  of  the  Malpighian 


Chap,  xxx.]    Kidney,  Ureter,  and  Bladder.      229 

corpuscles,  whence  it  travels  into  the  labyrinth  of 
minute  spaces  in  the  honeycombed  pulp  matrix  ; 
thence  it  passes  into  the  venous  sinuses,  and  finally 
into  the  venous  trunks.  The  current  of  blood  on  its 
passage  through  the  pulp  tissue  becomes,  therefore, 
greatly  retarded.  Under  these  conditions  numerous 
red  blood-corpuscles  appear  to  be  taken  up  by  the 
cells  of  the  pulp,  some  of  which  contain  several 
in  their  interior.  In  these  corpuscles  the  blood-discs 
become  gradually  broken  up,  so  that,  finally,  only 
granules  and  small  clumps  of  blood-pigment  are  left 
in  them.  The  presence  of  blood-pigment  in  the  cor- 
puscles of  the  pulp  is  explained  in  this  way ;  and  it  is 
therefore  said  that  the  pulp  tissue  is  a  destroyer  of 
red  blood-corpuscles. 

The  pulp  tissue  is  most  probably  the  birthplace  of 
colourless  blood-corpuscles  ;  and  according  to  Bizzozero 
and  Salvioli  it  is  also  the  birthplace  of  red  blood- 
corpuscles. 

The  lymphatics  form  plexuses  in  the  capsule 
(Tomsa,  Kyber).  These  are  continuous  with  the  plexus 
of  lymphatics  of  the  trabecule ;  and  these  again  with 
the  plexus  of  lymphatics  in  the  adventitia  of  the 
arterial  trunks. 

JVon-mechdlated  nerve-fibres  have  been  traced  along 
the  arterial  branches. 


CHAPTER  XXX. 

THE    KIDNEY,    URETER,    AND    BLADDER. 

300.    A.     The    framework. 

The  kidney  possesses  a  thin  investing  capsule  com- 
posed of  fibrous  tissue,  more  or  less  of  a  lamellar 
arrangement.     Bundles    of    fibrous   tissue  pass   with 


230  Elements  of  Histology.     [Chap.  xxx. 

blood-vessels  between  the  deeper  part  of  the  capsule 
and  the  parenchyma  of  the  periphery.  According 
to  Eberth,  a  plexus  of  non-striped  muscle  cells  is 
situated  underneath  the  capsule. 

The  ureter  entering  the  hilum  enlarges  into  the 
pelvis  of  the  kidney,  and  with  its  minor  recesses  or 
prolongations  forms  the  calices.  Both  the  pelvis  and 
the  calices  are  limited  by  a  wall  which  is  a  direct  con- 
tinuation of  the  ureter.  The  internal  free  surface  is 
lined  with  stratified  transitional  epithelium.  Under- 
neath the  epithelium  is  a  fibrous  connective  tissue 
membrane  (the  mucosa),  containing  the  networks  of 
capillary  blood-vessels  and  fine  nerve-fibres.  Outside 
the  mucosa  and  insensibly  passing  into  it  is  the 
loose-textured  submucosa,  with  groups  of  fat  cells. 
There  are  present  in  the  sub-mucosa  bundles  of 
non-striped  muscular  tissue,  continued  from  the 
ureter,  in  the  shape  of  longitudinal  and  circular 
bundles. 

In  the  pelvis  of  the  kidney  of  the  horse  small 
glands  (simple  or  branched  tubes),  lined  with  a  single 
layer  of  columnar  epithelial  cells,  have  been  observed 
by  Paladino,  Sertoli,  and  Egli.  The  last-named 
mentions  also  that  in  the  pelvis  of  the  human  kidney 
there  are  gland-tubes  similar  in  structure  to  sebaceous 
follicles. 

301.  The  large  vascular  trunks  enter,  or  pass  from 
the  tissue  of  the  calices  into  the  parenchyma  of  the 
kidney  between  the  cortex  and  medulla,  and  they  are 
accompanied  by  bundles  of  fibrous  connective  tissue 
and  here  and  there  a  few  longitudinal  bundles  of  non- 
striped  muscular  tissue. 

In  the  parenchyma  there  is  a  very  scanty 
fibrous  connective  tissue,  chiefly  around  the  Mal- 
pighian  corpuscles  and  around  the  arterial  vessels, 
especially  in  the  young  kidney.  In  the  papillae  there 
is  relatively  a  great  amount  of  fibrous  tissue.      On 


Chap,  xxx.]    Kidney ;  Ureter,  and  Bladder.      231 

the  surface  of  the  papillae  (facing  the  calices)  there 
is  a  continuous  layer  of  fibrous  tissue,  and  this  on 
its  free  surface  is  covered  with  stratified  transitional 
epithelium. 

The  parenchyma  of  the  kidney  consists  entirely  of 
the  urinary  tubules  and  the  intertubular  blood-vessels, 
and  there  is  an  interstitial  or  intertubular  connective 
tissue  framework  in  the  shape  of  honeycombed  hyaline 
membranes  with  flattened  nucleated  branched  or 
spindle-shaped  cells.  The  meshes  of  the  honeycomb 
are  the  spaces  for  the  urinary  tubules  and  blood- 
vessels. 

302.  B.  The  parenchyma. — I.  The  urinary 
tubules  (Fig.  133). — In  a  transverse  or  longitudinal 
section  through  the  kidney  we  notice  the  cortex,  the 
boundary  layer  of  Ludwig  and  the  papillary  portions, 
the  last  terminating  in  the  conical  papillai  in  the  cavity 
of  the  calices. 

The  boundary  layer  and  the  papillary  portion 
form  the  medulla.  A  papilla  with  the  papillary 
portion  and  boundary  layer,  continuous  with  it,  con- 
stitute a  Malpighian  "pyramid.  The  relative  propor- 
tion of  the  thickness  of  the  three  parts  is  about  3*5 
cortex,  2  5  boundary  layer,  and  4  papillary  portion. 

303.  The  cortex  consists  of  vast  numbers  of  con- 
voluted tubules  with  their  caecal  origin,  the  Mal- 
pighian corpuscle ;  this  is  the  labyrinth  separated  into 
vertical  divisions  of  equal  breadth  by  regularly  disposed 
vertical  straight  striae  originating  a  short  distance  from 
the  outer  capsule,  and  radiating  towards  the  boundary 
layer  which  they  enter.  Each  of  these  striae  is  a  bundle 
of  straight  tubules,  and  represents  a  medullary  ray. 
The  boundary  layer  shows  a  uniform  longitudinal  stria- 
tion,  in  which  opaque  and  transparent  striae  alternate 
with  one  another.  The  opaque  striae  are  continuations 
of  the  medullary  rays,  the  transparent  striae  are 
bundles  of  blood-vessels. 


Fig.  133. — Diagram  showing  the  course  of  the  Uriniferous  Tubules  in 
the  different  parts  of  the  Cortex  and  Medulla. 

(For  description  of  Fig.  133,  see  foot  of  next  page.) 


chap,  xxx.]    Kidney,  Ureter,  and  Bladder.      233 

The  papillary  portion  is  uniformly  and  longi- 
tudinally striated. 

Tracing  a  medullary  ray  from  the  boundary  layer 
into  the  cortex,  it  is  seen  that  its  breadth  gradually 
diminishes,  and  it  altogether  ceases  at  a  short  distance 
from  the  outer  capsule.  A  medullary  ray  is,  con- 
sequently, of  a  conical  shape,  its  apex  being  situated 
at  the  periphery  of  the  cortex,  its  base  in  the 
boundary  layer.  Such  a  pyramid  is  called  a  pyramid 
of  Ferrein. 

304.  All  urinary  tubules  commence  as  convoluted 
tubules  in  the  part  of  the  cortex  named  the 
labyrinth,  but  not  in  the  medullary  rays,  with  a 
csecal  enlargement  called  a  Malpighian  corpuscle,  and 
terminate — having  previously  joined  with  many  other 
tubules  into  larger  and  larger  ducts — at  one  of  the 
many  minute  openings  or  mouths  at  the  apex  of  a 
papilla.  On  their  way  the  tubes  several  times  alter 
their  size  and  nature. 

From  its  start  to  its  end  there  is  a  continuous 
fine  membrana  propria  forming  the  boundary  wall 
of  the  urinary  tubule,  and  this  membrana  propria  is 
lined  with  a  single  layer  of  epithelial  cells  differing  in 
size,  shape,  and  structure  from  place  to  place ;  in 
the  centre  of  the  tubule  is  a  lumen,  differing  in  size 
according  to  the  size  of  the  tubule. 

305.  (1)  Each  Malpighian  corpuscle  (Fig.  134) 
is  composed  of  the  capsule — the  capsule  of  Bowman — • 
and  the  glomerulus,  or  Malpighian  tuft  of  capillary 
blood-vessels. 


a,  Cortex  limited  on  its  free  surface  by  the  capsule ;  a,  subcapsular  layer  not 
containing  Malpighian  corpuscles;  a',  inner  stratum  of  cortex  without 
Malpighian  corpuscles ;  b,  boundary  layer ;  c,  papillary  part  next  the 
boundary  layer:  1,  Bowman's  capsule :  2,  neck  of  capsule ;  3,  proximal  con- 
voluted tube  ;  4,  spiral  part ;  5,  descending  limb  of  Henle's  loop-tube  ;  6, 
the  loop  itself  ;  7,  8,  and  9,  the  ascending  limb  of  Henle's  loop-tube ;  10,  the 
irregular  tubule  ;  11,  the  distal  convoluted  tubule ;  12,  the  first  part  of  the 
collecting  tube  ;  13  and  14,  larger  collecting  tube ;  in  the  papilla  itself,  not 
represented  here,  the  collecting  tube  joins  others,  and  forms  the  duct. 
,  (Atlas.) 


234 


Elements  of  Histology.      [Chap.  xxx. 


The  capsule  of  Bowman  is  a  hyaline  membrana 
propria,  supported,  as  mentioned  above,  by  a  small 
amount  of  connective  tissue.  On  its  inner  surface 
there  is   a   continuous  layer  of   nucleated   epithelial 


Fig.  134— From  a  Section  through,  the  Cortical  Substance  of  the 
Kidney  of  a  Human  Foetus,  showing  a  Malpighian  corpuscle. 

a, Glomerulus ;  6,  tissue  of  the  glomerulus;  c,  epithelium  covering  the 
glomerulus  ;  d,  flattened  epithelium  lining  Bowman's  capsule;  e,  the 
capsule  itself ;  /,  uriniferous  tubules  in  cross  section.    (Handbook.) 


cells,  in  the  young  state  of  polyhedral  shape,  in  the 
adult  state  squamous. 

The  glomerulus  is  a  network  of  convoluted 
capillary  blood-vessels,  separated  from  one  another 
by  scanty  connective  tissue,  chiefly  in  the  shape 
of  a  few  connective  tissue  corpuscles.  The  capil- 
laries are  grouped  together  in  two  to  five  lobules. 
The  whole  surface  of  the  glomerulus  is  lined  with 
a  delicate  membrana  propria,  and  a  continuous  layer 


chap,  xxx.]    Kidney,  Ureter,  and  Bladder.      235 

of  nucleated  epithelial  cells,  polyhedral,  or  even 
columnar  in  the  young,  squamous  in  the  adult  state. 
The  membrana  propria  and  epithelium  dip  in,  of 
course,  between  the  lobules  of  the  glomerulus,  and 
represent  in  reality  the  visceral  layer  of  the  capsule 
of  the  Malpighian  corpuscle,  the  capsule  of  Bowman 
being  the  parietal  layer.  The  glomerulus  is  connected 
at  one  pole  with  an  afferent  and  efferent  arterial 
vessel,  the  former  being  the  larger. 

Between  Bowman's  capsule  and  the  glomerulus 
there  is  a  space,  the  size  of  which  differs  according 
to  the  state  of  secretion,  being  chiefly  dependent  on 
the  amount  of  fluid  present. 

The  Malpighian  corpuscles  are  distributed  in  the 
labyrinth  of  the  cortex  only,  with  the  exception  of  a 
thin  peripheral  layer  near  the  outer  capsule,  and  a 
still  thinner  layer  near  the  boundary  layer.  The 
Malpighian  corpuscles  near  the  boundary  layer  are  the 
largest,  those  near  the  periphery  the  smallest ;  in 
the  human  kidney  their  mean  diameter  is  about  y^ 
of  an  inch. 

306.  On  the  side  opposite  to  that  where  the 
afferent  and  efferent  arterioles  join  the  glomerulus, 
the  capsule  of  Bowman  passes  through  a  narrow  neck 
into  the  cylindrical  urinary  tubule  in  such  a  way, 
that  the  membrana  propria  and  epithelium  of  the 
capsule  are  continued  as  the  membrana  propria  and 
lining  epithelium  of  the  tubule  respectively,  and 
the  space  between  the  capsule  of  Bowman  and 
the  glomerulus  becomes  the  cavity  or  lumen  of  the 
urinary  tubule. 

307.  (2)  After  it  has  passed  the  neck,  the  urinary 
tubule  becomes  convoluted ;  this  is  the  proximal  con- 
voluted tubule  (Fig.  135).  It  is  of  considerable  length 
and  is  situated  in  the  labyrinth.  It  has  a  distinct 
lumen,  and  its  epithelium  is  a  single  layer  of  polyhedral 
or  short,  columnar,  angular,  or  club-shaped  cells,  each 


236 


Elements  of  Histology,     [chap.  xxx. 


with  a  spherical  nucleus.     These  cells  commence  gene- 
rally at  the  neck,  but  in  some  animals — e.g.,  in  the 


Fig.  135. — From  a  Vertical  Section  through,  the  Kidney  of  Dog,  showing 
part  of  the  Labyrinth  and  the  adjoining  Medullary  Ray. 

a,  The  capsule  of  Bowman ;  the  capillaries  of  the  glomerulus  are  arranged  in 
lobules;  n,  neck  of  capsule;  b,  irregular  tubule;  c,  proximal  convoluted 
tubules ;  d,  a  collecting  tube  ;  e,  part  of  the  spiral  tubule  ;  /,  portion  of  the 
ascending  limb  of  Henle's  loop-tube ;  d,  e,  /  form  the  medullary  ray. 
(Atlas.) 


mouse — they  already  have   begun  in  the  Malpighian 
corpuscle.     The  outer  part  of  the  cell  protoplasm — i.e., 


chap,  xxx.]    Kidney,  Ureter,  and  Bladder.      237 

next  the  membrana  propria — is  distinctly  striated, 
owing  to  the  presence  of  rod-shaped  fibrils  (Heiden- 
hain)  vertically  arranged.  The  inner  part  of  the  cell 
substance — i.e.,  between  the  nucleus  and  the  inner 
free  margin — appears  granular.  Epithelial  cells  the 
protoplasm  of  which  possesses  the  above  rod-shaped 
fibrils,  will  in  the  following  paragraphs  be  spoken  of 
as  fibrillated  cells. 

The  proximal  convoluted  tube  appears  sometimes 
thicker  than  at  other  times ;  in  the  first  case,  its 
lumen  is  smaller,  but  its  lining  epithelial  cells  are 
distinctly  more  columnar.  This  state  is  probably  con- 
nected with  the  state  of  secretion. 

308.  (3)  The  convoluted  tube  passes  into  the 
spiral  tubide  (Schachowa).  This  differs  from  the 
former  in  being  situated  not  in  the  labyrinth,  but  in 
a  medullary  ray,  in  which  it  forms  one  conspicuous 
element,  and  in  not  being  convoluted,  but  more  or 
less  straight,  slightly  wavy,  and  spiral.  Its  thickness 
and  lumen  are  the  same  as  in  the  former ;  its 
epithelium  is  a  single  layer  of  polyhedral  cells,  with 
distinct  indication  of  fibrillation. 

309.  (4)  Precisely  at  the  line  where  the  cortex 
joins  the  boundary  layer,  the  spiral  tube  becomes 
suddenly  greatly  reduced  in  thickness ;  it  becomes  at 
the  same  time  very  transparent;  its  lumen  is  distinct; 
its  membrana  propria  is  now  lined  with  a  single 
layer  of  scales,  each  with  an  oval  flattened  nucleus. 
This  altered  tubule  is  the  descending  loop-tube  of 
Henle,  and  it  pursues  its  course  in  the  boundary 
layer  as  a  straight  tubule,  in  the  continuation  of  the 
medullary  ray. 

In  aspect  and  size  this  part  of  the  urinary 
tubule  resembles  a  capillary  blood-vessel,  but  differs 
from  it  inasmuch  as,  in  addition  to  the  lining  layer 
of  flattened  epithelial  cells,  it  possesses  a  membrana 
propria. 


238  Elements  of  Histology.     [Chap.  xxx. 

310.  (5)  The  so  formed  descending  Henle's  loop- 
tube  passes  the  line  between  the  boundary  layer 
and  papillary  portion,  and  having  entered  this 
latter  pursues  its  course  for  a.  short  distance,  when 
it  sharply  bends  backwards  as  the  loop  of  Henle's 
tube ;  it  now  runs  back  towards  the  boundary  layer, 
and  precisely  at  the  point  of  entering  this  becomes 
suddenly  enlarged.  "Up  to  this  point  the  structure 
and  size  of  the  loop  are  exactly  the  same  as  those  of 
the  descending  limb. 

311.  (6)  Having  entered  the  boundary  layer  it 
pursues  its  course  in  this  latter  to  the  cortex  in  a 
more  or  less  straight  direction  within  the  medullary 
ray  as  the  ascending  loop-tube.  Besides  being  bigger 
than  the  descending  limb  and  the  loop,  its  lumen 
is  comparatively  smaller,  and  its  lining  epithelium 
is  a  layer  of  polyhedral,  distinctly  nbrillated 
epithelial  cells.  The  tube  is  not  quite  of  the-  same 
thickness  all  along  the  boundary  layer,  but  is  broader 
in  the  inner  than  in  the  outer  half;  besides,  the  tube 
is  not  quite  straight,  but  slightly  wavy  or  even 
spiral. 

(7)  Having  reached  the  cortex,  it  enters  this  as  the 
cortical  part  of  the  ascending  loop-tube,  forming  one 
of  the  tubes  of  a  medullary  ray ;  it  is  at  the  same 
time  narrower  than  in  the  boundary  layer,  and  is 
more  or  less  straight  or  wavy.  Its  lumen  is  very 
minute,  its  lining  cells  are  flat  polyhedral  with  a 
small  flattened  nucleus,  and  there  is  an  indication  of 
fibrillation  (Fig.  135). 

(8)  Sooner  or  later  on  its  way  in  the  cortex  in 
a  medullary  ray  it  leaves  this  latter  to  enter  the 
labyrinth,  where  it  winds  between  the  convoluted 
tubes  as  an  angular  irregular  tubule  (Fig.  135).  Its 
shape  is  very  irregular,  its  size  alters  from  place 
to  place,  its  lumen  is  very  minute,  its  epithelium  a 
layer  of  polyhedral,  pyramidal,  or  short  columnar  cells 


chap,  xxx.]    Kidney,  Ureter,  and  Bladder.      239 

— according  to  the  thickness  of  the  tube ;  each  cell 
possesses  a  flattened  oval  nucleus  next  to  the  lumen, 
and  a  very  coarsely  and  conspicuously  fibrillated  pro- 
toplasm. 

312.  (9)  This  irregular  tubule  passes  into  the 
distal  convoluted  tubule  or  intercalated  tubule  of 
Schweisfsrer  Seidel.  This  forms  one  of  the  convoluted 
tubes  of  the  labyrinth,  and  in  size,  aspect,  and 
structure,  is  identical  with  the  proximal  convoluted 
tubule. 

(10)  The  distal  convoluted  tube  passes  into  a 
short,  thin,  more  or  less  curved  or  wavy  collecting 
tubule,  lined  with  a  layer  of  transparent,  flattened, 
polyhedral  cells ;  this  is  still  contained  in  the  laby- 
rinth. 

(11)  This  leads  into  a  somewhat  larger  straight 
collecting  tube,  lined  with  a  layer  of  transparent  poly- 
hedral cells  and  with  distinct  lumen.  This  tube 
forms  part  of  a  medullary  ray,  and  on  its  way  to  the 
boundary  layer  takes  up  from  the  labyrinth  numerous 
curved  collecting  tubules. 

(12)  It  then  passes  unaltered  as  a  straight  collect- 
ing tube  through  the  boundary  layer  into  the  papillary 
portion. 

313.  (13)  In  this  part  these  tubes  join  under  acute 
angles,  thereby  gradually  enlarging.  They  run  in  a 
straight  direction  towards  the  apex  of  the  papilla, 
and  the  nearer  to  this  the  fewer  and  the  bigger  they 
become.  These  are  the  ducts  or  tubes  of  Bellini. 
They  finally  open  on  the  apex  into  a  calix.  The  lumen 
and  the  size  of  the  lining  epithelial  cells — viz.,  whether 
more  or  less  columnar — are  in  direct  relation  to  the  size 
of  the  collecting  tube.  The  substance  of  the  epi- 
thelial cells  is  a  transparent  protoplasm,  and  the 
nucleus  is  more  or  less  oval. 

314.  In  many  places  nucleated  cells,  spindle- 
shaped  or  branched,  can  be  traced  from  the  membrana 


240  Elements  of  Histology.     [Chap.  xxx. 

propria  of  the  tubule  between  the  lining  epithelium ; 
and,  in  some  cases,  even  a  delicate  nucleated  membrane 
can  be  seen  lining  the  surface  of  the  epithelium  next 
the  lumen.  In  the  frog,  the  epithelium  lining,  the 
Malpighian  corpuscles,  and  the  exceedingly  long  neck 
of  the  urinary  tubule,  are  possessed  of  long  filamentous 
cilia,  rapidly  moving  during  life.  In  the  neck  of 
some  of  the  urinary  tubules  in  mammals  there  is 
also  an  indication  of  cilia  to  be  noticed. 

Heidenhain  has  shown  that  indigo- sulphate  of 
sodium,  injected  into  the  circulating  blood  of  the  dog 
and  rabbit,  is  excreted  through  certain  parts  of  the 
urinary  tubules  only — viz.,  those  which  are  lined 
with  "fibrillated"  epithelium.  He  maintains  that 
this  excretion  is  effected  through  the  cell  sub- 
stance ;  but,  in  the  case  of  carmine  being  used  as 
pigment,  I  have  not  found  the  excretion  to  take  place 
through  the  substance  of  the  epithelial  cells,  but 
through  the  homogeneous  interstitial  or  cement  sub- 
stance between  the  epithelial  cells. 

315.  II.   The  blood-vessels  (Fig.  136). 

The  large  branches  of  the  renal  artery  and  vein 
are  situated  in  the  submucous  tissue  of  the  pelvis, 
and  they  enter,  or  pass  out  respectively  from,  the  part 
of  the  parenchyma  corresponding  to  the  junction  of 
the  cortex  and  boundary  layer,  where  they  follow  a 
more  or  less  horizontal  course,  and  give  off,  or  take  up 
respectively,  smaller  branches  to  or  from  the  cortex 
and  medulla. 

(1)  In  the  cortex  the  arterial  trunks  give  off  to 
the  cortex  small  branches,  which  singly  enter  tlie 
labyrinth  in  a  direction  vertical  to  the  surface  of  the 
kidney.  These  are  the  interlobular  arteries.  Each  of 
these,  on  its  way  towards  the  external  capsule  of  the 
kidney,  gives  off,  on  all  sides  of  its  circumference, 
shorter  or  longer  lateral  branches;  these  are  the 
afferent  arterioles  for  the  Malpighian  corpuscles,  each 


chap,  xxx.]  Kidney,   Ureter,  and  Bladder.     241 


one  entering  a  Malpighian 
corpuscle  and  breaking  up 
into  the  capillaries  of  the 
glomerulus. 

On  its  way  towards 
the  external  capsule,  the 
interlobular  arteries  be- 
come greatly  reduced,  and 
finally  enter  the  capillary 
network  of  the  most  peri- 
pheral part  of  the  cortex ; 
but  some  of  these  arterioles 
may  be  also  traced  into  the 
outer  capsule,  where  they 
become  connected  with  the 
capillary  networks  of  this 
latter.  The  efferent  vessel 
of  a  Malpighian  glome- 
rulus at  once  breaks  up 
into  a  dense  network  of 
capillary  blood  -  vessels, 
which  entwine  in  all  pos- 
sible directions  the  urinary 
tubules  of  the  labyrinth. 
This  network  is  continued 
with  that  of  capillaries  of 
the  medullary  rays,  the 
meshes  being  there  elon- 
gated, and  the  capillary 
blood-vessels,  for  obvious 
reasons,  more  of  a  straight 


ai,  Interlobular  artery  ;  vi,  interlobular 
vein  ;  g,  glomerulus  of  Malpighian 
corpuscle ;  vs,  vena  stellata ;  ar, 
arteria?  recta? ;  vr,  vena?  recta? ;  ab, 
bundle  of  arteriae  recta? ;  vb,  bundle 
of  vena?  recta? ;  vp,  network  of  vessels 
around  the  mouth  of  the  ducts 
at  the  apex  of  the  papilla?.  (Ludwig, 
in  Strieker's  Manual.) 


Fig.  136. — Diagram  of  the  Vessels 
of  the  Kidney. 


242  Elements  of  Histology.      [Chap.  xxx. 

arrangement.       The  capillaries  of    the  whole    cortex 
form  one  continuous  network. 

316.  The  veins  which  take  up  the  blood  from  this 
network  are  arranged  in  this  manner  : — There  are 
formed  venous  vessels  underneath  the  external 
capsule,  taking  up  like  rays  on  all  sides,  minute 
radicles  connected  with  the  capillaries  of  the  most 
peripheral  part  of  the  cortex.  These  are  the  vence 
stellatw;  they  pass  into  the  labyrinth  of  the 
cortex,  where  they  follow  a  vertical  course  in 
company  with  the  interlobular  arteries.  On  the 
way  they  communicate  with  the  capillaries  of  the 
labyrinth,  and  ultimately  open  into  the  large 
venous  branches  situated  between  cortex  and  boun- 
dary layer. 

317.  (2)  In  the  medulla.  From  the  large  arterial 
trunks  short  branches  come  off,  which  enter  the 
boundary  layer,  and  there  split  up  into  a  bundle 
of  minute  arterioles,  which  pass  in  a  straight  direc- 
tion vertically  through  the  boundary  layer  into  the 
papillary  portion.  These  are  the  arterice  rectce 
(Fig.  136).  The  number  of  vessels  of  each  bundle 
is  at  the  outset  increased  by  the  efferent  vessel  of 
the  Malpighian  corpuscles  nearest  to  the  boundary 
laver. 

On  their  way  through  the  boundary  layer,  and 
through  the  papillary  portion  of  the  medulla, 
these  arterioles  give  off  the  capillary  network  for 
the  urinary  tubules  of  these  parts,  the  network, 
for  obvious  reasons,  possessing  an  elongated  arrange- 
ment. 

From  this  network  originate  everywhere  minute 
veins,  which  on  their  way  towards  the  cortical  margin 
increase  in  size  and  number ;  they  form  also  bundles 
of  straight  vessels — vence  rectce — and  ultimately  enter 
the  venous  trunks  situated  between  the  boundary 
layer  and  cortex. 


Chap,  xxx.]  Kidney,  Ureter,  and  Bladder.        243 

The  bundles  of  the  arteriae  rectse  and  venae 
rectae  form  severally,  in  the  boundary  layer,  the 
transparent  striae  mentioned  on  a  previous  page  as 
alternating  with  the  opaque  striae,  these  latter  being 
bundles  of  urinary  tubules. 

At  the  apex  of  each  papilla  there  is  a  network 
of  capillaries  around  the  mouth  of  each  duct. 

318.  The  outer  capsule  of  the  kidney  contains  a 
network  of  capillary  blood-vessels ;  the  arterial 
branches  leading  into  them  are  derived  from  two 
sources  :  (a)  from  the  outrunners  of  the  interlobular 
arteries  of  the  cortex,  and  (b)  from  extrarenal  arteries. 
The  veins  lead  («)  into  the  venae  stellatae,  and  (b)  the 
extrarenal  veins. 

The  lymphatic  vessels  form  a  plexus  in  the  capsule 
of  the  kidney.  They  are  connected  with  lymph 
spaces  between  the  urinary  tubes  of  the  cortex. 
The  large  blood-vessels  are  surrounded  by  a  plexus  of 
lymphatics,  which  take  up  lymph  spaces  between  the 
urinary  tubules,  both  in  the  cortex  and  the  boundary 
layer. 

319.  The  ureter  is  lined  with  stratified  transi- 
tional epithelium.  Underneath  this  is  the  mucosa, 
a  connective  tissue  membrane  with  capillary  blood- 
vessels. The  submucosa  is  a  loose  connective  tissue 
Then  follows  a  muscular  coat  composed  of  non- 
striped  muscular  tissue,  arranged  as  an  inner  and 
outer  longitudinal  and  a  middle  circular  coat.  Then 
follows  an  outer  limiting  thin  fibrous  coat  or  adventitia. 
In  this  last  have  been  observed  minute  ganglia  in 
connection  with  the  nerve  branches. 

320.  The  bladder  is  similar  in  structure,  but  the 
mucous  membrane  and  muscular  coat  are  very  much 
thicker.  In  the  latter,  which  consists  of  non-striped 
fibres,  are  distinguished  an  inner  circular,  a  middle 
oblique,  and  an  outer  longitudinal  stratum.  The 
last  is  best  developed  in  the  fundus. 


244  Elements  of  Histology.     [Chap.  xxxi. 

Numerous  sympathetic  ganglia,  of  various  sizes, 
are  found  in  connection  with  the  nerve  branches  un- 
derneath the  adventitia  (peritoneal  covering),  and  in 
the  muscular  coat  (F.  Darwin).  The  epithelium  lining 
the  bladder  is  stratified  transitional,  and  it  greatly 
varies  in  the  shape  of  its  cells  and  their  stratification, 
according  to  the  state  of  expansion  of  the  bladder. 


CHAPTER   XXXL 

THE  MALE  GENITAL  ORGANS. 

321.  (1)  The  testis  of  man  and  mammals  is  en- 
veloped in  a  capsule  of  white  fibrous  tissue,  the  tunica 
adnata.  This  is  the  visceral  layer  of  the  tunica 
vaginalis.  Like  the  parietal  layer,  it  is  a  serous 
membrane,  and  is  therefore  covered  with  endo- 
thelium. Minute  villi  are  occasionally  seen  pro- 
jecting from  this  membrane  into  the  cavity  of 
the  tunica  vaginalis.  These  villi  are  generally 
covered  with  germinating  endothelium  (see  par.  33). 
Inside  the  tunica  adnata,  and  firmly  attached  to 
it,  is  the  tunica  albuginea,  a  fibrous  connective 
tissue  membrane  of  lamellar  structure.  Towards 
the  posterior  margin  of  the  human  testis  its  thick- 
ness increases,  and  forms  there  a  special  accumu- 
lation— in  cross  section  more  or  less  conical,  with 
posterior  basis — the  mediastinum  testis,  or  corpus 
Highmori. 

Between  the  tunica  adnata  and  tunica  albuginea 
is  a  rich  plexus  of  lymphatics,  which,  on  the  one  hand, 
takes  up  the  lymphatics   of  the  interior,  and  on   the 


chap,  xxxi.]  The  Male  Genital  Organs.  245 

other  leads  into  the  efferent  vessels  that  accompany 
the  vas  deferens. 

The  testis  of  the  dog,  cat,  bull,  pig,  rabbit,  &c, 
have  a  central  corpus  Highmori ;  that  of  the  mole, 
hedgehog,  and  bat  a  peripheral  one ;  while  that  of  the 
rat  and  mouse  have  none  (Messing). 

322.  The  framework. —  From  the  anterior 
margin  of  the  corpus  Highmori  spring  numerous 
septa  of  connective  tissue,  which,  passing  in  a  radiat- 
ing direction  towards  the  albuginea,  with  which  they 
form  a  continuity,  subdivide  the  testis  into  a  large 
number  of  long,  conical  compartments,  or  lobules, 
the  basis  of  which  is  situated  at  the  tunica  albu- 
ginea, the  apex  at  the  corpus  Highmori.  Kolliker 
mentions  that  non-striped  muscular  tissue  occurs  in 
these  septa. 

From  these  septa  thin  connective  tissue  lamellae 
pass  into  the  compartments,  and  they  form  the  sup- 
porting tissue  for  the  blood-vessels  and  also  represent 
the  interstitial  connective  tissue  between  the  seminal 
tubules. 

This  intertubular  or  interstitial  tissue  is  distinctly 
lamellated,  the  lamellae  being  of  different  thicknesses, 
and  consisting  of  thin  bundles  of  fibrous  connective 
tissue — arranged  more  or  less  as  fenestrated  mem- 
branes— and  endotheloid  connective  plates  on  their 
surface.  Between  the  lamellae  are  left  spaces,  and 
these  form,  through  the  fenestrae  or  holes  of  the 
lamellae,  an  intercommunicating  system  of  lymph 
spaces — being,  in  fact,  the  rootlets  of  the  lymphatics 
(Ludwig  and  Tomsa). 

Within  the  lamellae  are  found  peculiar  cells, 
which  are  much  larger  than  lymph-cells,  and  which,  in 
some  instances  (e.g.,  guinea-pig),  include  pigment 
granules.  They  contain  a  spherical  nucleus.  In  man, 
in  dog,  cat,  sheep,  especially  boar,  these  cells  form 
large,  continuous  groups — plates  and  cylinders — and 


246 


Elements  of  Histology.     [ChaP:xxxi. 


the  cells  are  polyhedral,  and  exactly  similar  to  epithe- 
lial cells.  They  are  separated  from  one  another  within 
the  group  by  a  thin  interstitial  cement- substance. 
Their  resemblance  with  epithelium  is  complete.  They 
are  remnants  of  the  epithelial  masses  of  the  Wolffian 
body  of  the  foetus. 

323.    The     seminal    tubules     (Fig.     137).  — 
Within    each    compartment,     above    mentioned,     lie 


F;g.  137. — From  a  Section  through  the  Testis  of  Dog. 

Showing  three  seminal  tubules  in  cross  section.  In  two  of  these  the  lining 
epithelium— seminal  cells— is  shown,  and  bundles  of  spermatozoa  projecting 
into  the  lumen  of  the  tubules.  Between  the  tubules  is  connective  tissue 
containing  groups  of  polyhedral  epithelial-like  cells. 


numerous  seminal  tubules,  twisted  and  convoluted 
in  many  ways,  and  extending  from  the  periphery  to 
near  the  corpus  Highmori.  The  tubules,  as  a  rule, 
are  rarely  branched ;  but  in  the  young  state,  and 
especially  towards  the  periphery,  branching  is  not  un- 
common. 

Each  seminal  tubule  consists  of  a  membrana  pro- 
pria, a  lining  epithelium,  and  a  lumen.  The  mem- 
brana propria  is  a  hyaline  membrane,  with  oval  nuclei 
at  regular  intervals.  In  man  it  is  thick  and  lamel- 
lated,  several  such  nucleated  membranes  being  super- 


Chap,  xxxi.]  The  Male  Genital  Organs.  247 

imposed  over  one  another.  The  lumen  is  in  all  tubes 
distinct  and  relatively  large.  The  lining  epithelium, 
or  the  seminal  cells,  differ  in  the  adult  in  different 
tubules,  and  even  in  different  parts  of  the  same  tubule, 
being  dependent  on  the  state  of  secretion. 

324.  Before  puberty  all  tubules  are  uniform  in 
this  respect,  being  lined  with  two  or  three  layers  of 
polyhedral  epithelial  cells,  each  with  a  spherical 
nucleus.  After  puberty,  however,  the  following 
different  types  can  be  distinguished  : — 

(a)  Tubules  or  parts  of  tubules  similar  to  those 
of  the  young  state — viz.,  several  layers  of  polyhedral 
epithelial  cells  lining  the  membrana  propria.  These 
are  considered  as  (a)  the  outer  and  (b)  the  inner 
seminal  cells.  The  former  are  next  to  the  membrana 
propria ;  they  are  polyhedral  in  shape,  transparent, 
and  the  nucleus  of  some  of  them  is  in  the  process 
of  karyokinesis  or  indirect  division  (see  par.  8)  ; 
others  include  an  oval  transparent  nucleus.  The 
inner  seminal  cells  generally  form  two  or  three  layers, 
and  are  more  loosely  connected  with  one  another  than 
the  outer  seminal  cells,  and  therefore  possess  a  more 
rounded  appearance.  Between  these  a  nucleated  reti- 
culum of  fine  fibres  is  sometimes  noticed,  the  germ 
reticulum  of  von  Ebner.  But  this  is  merely  a  support- 
ing tissue,  and  has  nothing  to  do  with  the  germina- 
tion of  the  cells  or  the  spermatozoa  (Merkel).  The 
inner  seminal  cells  show  very  abundantly  the  process 
of  indirect  division  or  karyokinesis,  almost  all  being 
seen  in  one  or  other  phase  of  it. 

325.  In  consequence  of  this,  numerous  small 
spherical  daughter-cells  are  formed  ;  these  lie  nearest 
the  lumen,  and  are  very  loosely  connected  with  one 
another.  It  is  these  which  are  transformed  into  sper- 
matozoa, and  hence  are  appropriately  called  spermato- 
blasts (Fig.  137). 

Amongst  the  seminal  cells,  especially  of  cat  and 


248 


Elements  of  Histology.     [Chap.  xxxi. 


dog,  are  found  occasionally,  but  not  very  commonly, 
large  multinuclear  cells,  the  nuclei  of  which  are  also 
in  one  or  the  other  stage  of  karyokinesis. 

(b)  The  innermost  cells,  i.e.,  the   spermatoblasts, 
become  pear-shaped,  the  nucleus  being  situated  at  the 


Fig.  138. — From  a  Section  through  the  Testis  of  Dog,  showing 
portions  of  three  Seminal  Tubules. 

4.,  Seminal  epithelial  cells  and  numerous  small  cells  loosely  arranged;  b,  the 
small  cells  or  spermatoblasts  converted  into  spermatozoa;  c,  groups  of 
these  in  a  further  stage  of  development.  (Atlas.) 

thinner  extremity,  becoming  at  the  same  time  flattened 
and  homogeneous  (Fig.  138).  The  elongation  of  the 
spermatoblasts  gradually  proceeds,  and  in  consequence 
of  this  we  find  numerous  elongated,  club-shaped  sper- 
matoblasts, each  with  a  flattened  nucleus  at  the  thin 
end.  These  are  the  young  spermatozoa,  the  nucleated 
extremity  being  the  head. 

(c)  At  the  same  time  these  young  spermatozoa 
become  grouped  together  by  an  interstitial  granular 
substance,   in  peculiar   fan-shaped    groups ;    in    these 


Chap,  xxxi.]   The  Male  Genital  Organs.  249 

groups  the  head, — i.e.,  the  thin  end  containing  the 
flattened  homogeneous  nucleus, — is  directed  towards 
the  inner  seminal  cells,  while  the  opposite  extremity- 
is  directed  into  the  lumen  of  the  tube.  Meanwhile 
the  inner  seminal  cells  continue  to  divide,  and  thus 
the  groups  of  young  spermatozoa  get  more  and  more 
buried,  as  it  were,  between  them. 

326.  The  original  cell-body  of  the  spermatoblasts 
goes  on  elongating  until  its  protoplasm  is  almost,  but 
not  quite,  used  to  form  the  rod-shaped  middle  piece 
(Schweigger  Seidel)  of  the  spermatozoa ;  from  the 
distal  end  of  this,  a  thin  long  hair-like  filament,  called 
the  tail,  grows  out.  Where  this  joins  the  end  of  the 
middle  piece,  there  is,  even  for  some  time  afterwards, 
a  last  remnant  of  the  granular  cell-body  of  the  original 
spermatoblast  to  be  noticed. 

When  the  granular  interstitial  substance  holding- 
together  the  spermatozoa  of  a  group  has  become  dis- 
integrated, the  spermatozoa  are  isolated.  While  this 
development  of  the  spermatozoa  goes  on,  the  inner 
seminal  cells  continue  to  produce  spermatoblasts, 
which  in  their  turn  are  converted  into  spermatozoa. 

327.  Spermatozoa  (Fig-  139). — Fully  formed 
spermatozoa  of  man  and  mammals  consist  of  a  homo- 
geneous flattened  and  slightly  convex-concave  head  (the 
nucleus  of  the  original  spermatoblast),  a  rod-shaped 
middle  piece  (derived  directly  from  the  cell  body  of 
the  spermatoblast),  and  a  long  hair-like  tail.  WTiile 
living,  the  spermatozoa  show  very  rapid  oscillatory  and 
propelling  movement,  the  tail  acting  as  a  flagellum  or 
cilium  ;  its  movements  are  spiral. 

In  the  newt  there  is  a  fine  spiral  thread 
attached  to  the  end  of  the  long,  curved,  spike-like 
head,  and  by  a  hyaline  membrane  it  is  fixed  to  the 
middle  piece  ;  it  extends  beyond  this  as  the  long  thin 
tail.  Also  in  the  mammalian  and  human  sperma- 
tozoa, a  similar  spiral  thread,  closely  attached  to  the 


25° 


Elements  of  Histology.     [Chap.  xxxi. 


middle  piece,  and  terminating  as  the  tail,  has  been  ob- 
served (H.  Gibbes). 

328.  The  seminal  tubules  of  each  compartment 
or  lobule  empty  themselves  into  a  short,  more  or  less 
straight,   tubule — the  vas   rectum.      This  is  narrower 


Fig.  1S9. — Various  kinds  of  Spermatozoa. 

A,  Spermatozoon  of  guinea-pig  not  yet  completely  ripe ;  b,  the  same  seen  side- 
ways, the  head  of  the  spermatozoon  is  flattened  from  side  to  side ;  c,  a 
spermatozoon  of  the  horse  ;  d,  a  spermatozoon  of  the  newt. 

than  the  seminal  tubule,  and  is  lined  with  a  single 
layer  of  polyhedral  or  short  columnar  epithelial  cells. 
The  vasa  recta  form,  in  the  corpus  Highmori,  a  dense 
network  of  tubular  channels,  which  are  irregular  in 
diameter,  being  at  one  place  narrow  clefts,  at  another 
wide  tubes,  but  never  so  wide  as  the  seminal  tubules ; 
this  network  of  channels  is  the  rete  testis. 

329.   (2)  The  epididymis. — From  the  rete  testis 
we  pass  into  the  vasa  eferentia,  each   being  a  tube 


chap,  xxxi.]   The  Male  Genital  Organs. 


251 


wider  than  those  of  the  rete  testis,  and  each  leading  into 
a  conical  network  of  coiled  tubes.  These  are  the  coni 
vasculosis  The  sum  total  of  all  the  coni  vasculosi 
forms  the  globus  major  or  head  of  the  epididymis. 

330.  The  vasa  efferentia  and  the  tubes  of  the 
coni  vasculosi  are  about  the  size  of  the  seminal 
tubules,  but,  unlike  them,  are  lined  with  a  layer  of 
beautiful  columnar  epithelial  cells,  with  a  bundle  of 
cilia  (Fig.  140).  Outside 
these  is  generally  a  layer, 
more  or  less  continuous,  of 
small  polyhedral  cells.  The 
substance  of  the  columnar 
cells  is  distinctly  longitudi- 
nally fibrillated.  The  mem- 
brana  propria  is  thickened 
by  the  presence  of  a  cir- 
cular layer  of  non-striped 
muscular  fibres.  The  rest, 
i.e.,  the  globus  minor,  or 
tail  of  the  epididymis,  is 
made  up  of  a  continuation 
of  the  tubes  of  the  globus 
major,  the  tubes  diminish- 
ing gradually  in  number  by 

fusion,  and  at  the  same  time  thereby  becoming  larger. 
The  columnar  epithelial  cells,  facing  the  lumen  of  the 
tubes  of  the  globus  minor,  are  possessed  of  cilia  of 
unusual  length. 

The  tubes  of  the  epididymis  are  separated  from 
one  another  by  a  larger  amount  of  connective  tissue 
than  those  of  the  testis. 

The  tubes  of  the  organ  of  Giralde,  situated  in 
the  beginning  of  the  funiculus  spermaticus,  are  lined 
with  columnar  ciliated  epithelium.  So  is  also  the 
pedunculated  hydatid  of  Morgagni  attached  to  the 
globus  major. 


Fig.  140.— A  tubule  of  the  epi- 
didymis in  cross  section. 

The  wall  of  the  tubule  is  made  up  of 
a  thick  layer  of  concentrically  ar- 
ranged n<  n-striped  muscular  tissue, 
a  layer  of  columnar  epithelial  cells 
with  extraordinarily  long  cilia  pro- 
jecting into  the  lumen  of  the  tube. 


252  Elements  of  Histology.     [Chap.  xxxi. 

331.  The  seminal  tubules  and  the  tubes  of  the 
epididymis  are  entwined  by  a  rich  network  of 
capillary  blood-vessels.  Between  the  tubes  of  the 
testis  and  epididymis  are  lymph  spaces,  forming  an 
intercommunicating  system,  and  emptying  themselves 
into  the  superficial  networks  of  lymphatics,  i.e.,  those 
of  the  albuginea ;  the  arrangement  of  these  networks 
is  somewhat  different  in  the  testis  and  epididymis. 

332.  (3)  Tas  deferens  and  vesicular  semi- 
nales. — The  tubes  of  the  globus  minor  open  into  the 
vas  deferens.  This  is  of  course  much  larger  than 
the  former,  and  is  lined  with  stratified  columnar 
epithelium.  Underneath  this  is  a  dense  connective 
tissue  mucosa,  containing  a  rich  network  of  capillary 
blood-vessels.  Beneath  this  mucosa  is  a  thin  sub- 
mucous tissue,  which  in  the  Ampulla  is  better  de- 
veloped than  in  other  parts,  and  therefore  allows  the 
mucous  membrane  to  become  folded.  Outside  the  sub- 
mucous tissue  is  the  muscular  coat,  which  consists  of 
non-striped  muscular  tissue,  arranged  as  an  inner 
circular  and  an  outer  longitudinal  stratum.  At  the 
commencement  of  the  vas  deferens  there  is  in  addition 
an  inner  longitudinal  layer.  There  is  finally  a  fibrous 
tissue  adventitia.  This  contains  longitudinal  bundles 
of  non-striped  muscular  tissue,  known  as  the  cremaster 
intemus  (Henle).  A  rich  plexus  of  veins — plexus 
pampiniformis — and  a  rich  plexus  of  lymphatic  trunks, 
are  situated  in  the  connective  tissue  of  the  spermatic 
cord.  The  plexus  spermaticus  consists  of  larger  and 
smaller  nerve-trunks,  with  which  are  connected  small 
groups  of  ganglion  cells  and  also  large  ganglionic 
swellings. 

333.  In  the  vesiculce  seminales  we  meet  with 
exactly  the  same  layers  as  constitute  the  wall  of  the 
vas  deferens,  but  they  are  thinner.  This  refers  espe- 
cially to  the  mucosa  and  the  muscular  coat.  The 
former  is  placed  in  numerous  folds.     The  latter  con- 


chap,  xxxi.]   The  Male  Genital  Organs.  253 

sists  of  an  inner  and  outer  longitudinal  and  a  middle 
circular  stratum.  The  ganglia  in  connection  with  the 
nerve-trunks  of  the  adventitia  are  very  numerous. 

334.  In  the  ductus  ejaculatorii  we  find  a  lining  of 
columnar  epithelial  cells ;  outside  of  this  is  a  delicate 
mucosa  and  a  muscular  coat,  the  latter  consisting  of 
an  inner  thicker  longitudinal  and  an  outer  thinner 
circular  stratum  of  non-striped  muscular  tissue. 

When  passing  into  the  vesicula  prostatica  the 
columnar  epithelium  is  gradually  replaced  by  stratified 
pavement  epithelium. 

335.  (4)  The  prostate  gland.  —  Like  other 
glands,  the  prostate  consists  of  a  framework  and  the 
gland  tissue  proper  or  the  parenchyma. 

The  framework,  unlike  that  of  other  glands,  is 
essentially  muscular,  being  composed  of  bundles  of 
non-striped  muscular  tissue,  with  a  relatively  small 
admixture  of  fibrous  connective  tissue.  The  latter 
is  chiefly  limited  to  the  outer  capsule  and  the  thin 
septa  passing  inwards,  whereas  the  non-striped  mus- 
cular tissue  surrounds  and  separates  the  individual 
gland  alveoli. 

336.  The  parenchyma  consists  of  the  chief  ducts, 
which  open  at  the  base  of  and  near  the  colliculus 
seminalis,  and  of  the  secondary  ducts,  minor  branches 
of  the  former,  which  ultimately  lead  into  the  alveoli. 
These  are  longer  or  shorter,  wavy  or  convoluted 
branched  tubes  with  numerous  saccular  or  club-shaped 
branches.  The  alveoli  and  ducts  are  limited  by  a 
membrana  propria,  have  a  distinct  lumen,  and  are 
lined  with  columnar  epithelium.  In  the  alveoli  there 
is  only  a  single  layer  of  beautiful  columnar  epithelial 
cells,  the  substance  of  which  is  distinctly  and  longi- 
tudinally striated.  In  the  ducts  there  is  an  inner 
layer  of  short  columnar  cells,  and  an  outer  one  of 
small  cubical,  polyhedral  or  spindle-shaped  cells. 

At  the  mouth  of  the  ducts  the  stratified  pavement 


254  Elements  of  Histology.     [Chap.  xxxi. 

epithelium  of  the  pars  prostatica  of  the  urethra 
passes  a  short  distance  into  the  duct. 

The  alveoli  are  surrounded  by  dense  networks  of 
capillary  blood-vessels. 

In  the  peripheral  portion  of  the  gland  numerous 
ganglia  are  interjDOsed  in  the  rich  plexus  of  nerves. 
Also  Pacinian  corpuscles  are  to  be  met  with. 

337.  (5)  The  urethra. — The  mucous  membrane 
of  the  male  urethra  is  lined  with  simple  columnar 
epithelium,  except  at  the  commencement — the  pars 
prostatica — and  at  the  end — the  fossa  navicularis — 
where  it  is  stratified  pavement  epithelium. 

The  mucous  membrane  is  fibrous  tissue  with  very 
numerous  elastic  fibres.  Outside  of  it  is  a  muscular  coat 
composed  of  non-striped  muscular  tissue,  and  arranged 
as  an  inner  circular  and  an  outer  longitudinal  stratum, 
except  in  the  pars  prostatica  and  pars  membranacea, 
where  it  is  chiefly  longitudinal.  In  the  latter  portion 
the  muscular  bundles  pass  also  into  the  mucous  mem- 
brane, where  they  follow  a  longitudinal  course  between 
large  veins  arranged  in  a  longitudinal  plexus.  These 
veins  empty  themselves  into  small  veins  outside.  This 
plexus  of  large  veins  with  the  muscular  tissue  between 
represents  a  rudiment  of  a  cavernous  tissue  (Henle). 

The  mucous  membrane  forms  peculiar  folds  sur- 
rounding the  lacunae  Morgagni.  There  are  small  mucous 
glands,  lined  with  columnar  epithelium,  embedded  in 
the  mucous  membrane ;  they  open  into  the  cavity  of 
the  urethra  and  are  known  as  Littre's  glands. 

338.  (6)  The  glands  of  Cowper. — Each  gland 
of  Cowper  is  a  large  compound  tubular  gland,  which, 
as  regards  structure  of  ducts  and  alveoli,  resembles  a 
mucous  gland.  The  wall  of  the  chief  ducts  possesses 
a  large  amount  of  longitudinally-arranged  non-striped 
muscular  tissue.  The  epithelium  lining  the  ducts  is 
composed  of  columnar  cells.  The  alveoli  possess  a 
large    lumen    and  are    lined  with   columnar  mucous 


chap,  xxxi.]  The  Male  Genital  Organs.  255 

cells,  the  outer  portion  of  the  cell  being  distinctly 
striated  (Langerhans).  In  the  cell  the  reticulum  is 
also  distinct.  In  this  respect  the  alveoli  completely 
resemble  those  of  the  sub-maxillary  of  the  dog,  but 
there  are  no  real  crescents  in  the  alveoli  of  Cowper's 
gland. 

339.  (7)  The  corpus  spongiosum. — The  cor- 
pus spongiosum  of  the  urethra  is  a  continuation  of 
the  rudimentary  corpus  cavernosum  above-mentioned 
in  connection  with  the  pars  membranacea  of  the 
urethra.  It  is  essentially  a  plexus  of  large  veins 
arranged  chiefly  longitudinally  and  leading  into  small 
efferent  veins.  Between  the  large  veins  are  bundles 
of  non-striped  muscular  tissue.  The  capillary  blood- 
vessels of  the  mucous  membrane  of  the  urethra  open 
into  the  veins  of  the  plexus.  The  outer  portion  of 
the  corpus  spongiosum,  including  the  bulbus  urethras, 
shows,  however,  numerous  venous  sinuses,  real  caver- 
nse,  into  which  open  capillary  blood-vessels. 

340.  The  glans  penis  is  of  exactly  the  same 
structure  as  the  corpus  spongiosum.  The  outer  surface 
is  covered  with  a  delicate  fibrous  tissue  membrane, 
which  on  its  free  surface  bears  minute  papillae, 
extending  into  the  stratified  pavement  epithelium.  At 
the  corona  glandis  exist  small  sebaceous  follicles,  the 
glands  of  Tyson ;  they  are  continued  from  the  inner 
lamella  of  the  prepuce,  where  they  abound.  The 
papillae  of  the  glans  contain  loops  of  capillary  blood- 
vessels. Plexuses  of  non-medu  Hated  nerve-fibres  are 
found  underneath  the  epithelium  of  the  surface  of 
the  glans.  With  these  are  connected  the  end  bulbs 
described  in  a  former  chapter  as  the  genital  nerve-end 
corpuscles. 

341.  (8)  The  corpora  cavernosa  penis. — Each 
corpus  cavernosum  is  enveloped  in  a  fibrous  capsule, 
the  albuginea,  made  up  of  lamellae  of  fibrous  con- 
nective  tissue.      Numerous  Pacinian    corpuscles    are 


256  Elements  of  Histology.     [Chap.  xxxi. 

met  with  around  it.  The  matrix  of  the  corpus 
cavernosum  consists  of  trabecule  of  fibrous  tissue, 
between  which  pass  bundles  of  non-striped  muscular 
tissue  all  in  different  directions.  Innumerable 
cavernse  or  sinuses,  intercommunicating  with  one 
another,  are  present  in  this  matrix,  capable  of  such 
considerable  repletion,  that  in  the  maximum  degree 
of  this  state  the  sinuses  are  almost  in  contact, 
and  the  trabecule  compressed  into  very  delicate 
septa.  The  sinuses  are  lined  with  a  single  layer  of 
flattened  endothelial  plates,  and  their  wall  in  many 
places  is  strengthened  by  the  bundles  of  non-striped 
muscular  tissue.  The  sinuses  during  erection  become 
filled  with  blood,  being  directly  continuous  with  capil- 
lary blood-vessels.  These  are  derived  from  the  arte- 
rial branches  which  take  their  course  in  the  above 
trabecular  of  the  matrix.  The  blood  passes  from  the 
sinuses  into  small  efferent  veins.  But  the  blood 
passes  also  directly  from  the  capillaries  into  the 
efferent  veins,  and  this  is  the  course  the  blood  takes 
under  passive  conditions,  while  during  erection  it 
passes  chiefly  into  the  above  sinuses. 

342.  In  the  peripheral  part  of  the  corpus  caver- 
nosum there  exists  a  direct  communication  between  the 
sinuses  and  minute  arteries  (Langer),  but  in  the  rest 
the  arteries  do  not  directly  communicate  with  the 
sinuses  except  through  the  capillary  blood-vessels. 
In  the  passive  state  of  the  corpus  cavernosum,  the 
muscular  trabecular  forming  part  of  the  matrix  are 
contracted,  and  the  minute  arterial  branches  embedded 
in  them  are  therefore  much  coiled  up  ;  these  are  the 
arterise  helicinar. 


Chap.  XXXI I.J 


257 


CHAPTER   XXXII. 


THE    FEMALE    GENITAL    ORGANS. 

343.  (1)  The  ovary  (Fig.  141.) — In  the  ovary,  as 
in  other  glands,  the  framework  is  to  be  distinguished 
from  the  paren- 
chyma. In  the  part 
of  the  ovary  next 
to  the  hilum  there 
are  numerous  blood- 
vessels, in  a  loose 
fibrous  connective 
tissue,  with  nu- 
merous longitudinal 
bundles  of  non- 
striped  muscular 
tissue  directly  con- 
tinuous with  the 
same  tissues  of  the 
ligamentum  latum. 


■   .   .    ■.'.'   ■■'■'   ■      .■■,.,.■ 


Fig. 


*>:':" 


141. — Vertical    Section    through 
Ovary  of  half -grown  Cat. 


the 


This  portion  of  the 
ovary  is  the  zona 
vasculosa  (Wal- 
deyer).  All  parts  of 
the  zona  vasculosa 
— i.e.,  the  bundles 
of  fibrous  connec- 
tive tissue,  the 
blood  -  vessels,  and 
the  bundles  of  non- 
striped  muscular 
tissue — are  traceable  into  the  parenchyma.  The  stroma 
of  this  latter,  however,  is  made  up  of  bundles  of  shorter 

R 


a,  The  albuginea ;  tbe  germinal  epithelium  is  not 
distinguishable  owing  to  the  low  power  under 
which  the  section  is  supposed  to  be  viewed; 
b,  the  layer  of  smallest  Graafian  follicles  and 
ova  ;  c,  the  medium-sized  follicles  :  d,  the  layer 
of  large  follicles  ;  e,  the  zona  vasculosa.  (Atlas.) 


258  Elements  of  Histology.    [Chap,  xxxii. 

or  longer  transparent  spindle-shaped  cells,  each  with  an 
oval  nucleus.  These  bundles  of  spindle-shaped  cells 
form,  by  crossing  and  interlacing,  a  tolerably  dense 
tissue,  in  which  lie  embedded  in  special  arrangements 
the  Graafian  follicles.  Around  the  larger  examples  of 
the  latter  the  spindle-shaped  cells  form  more  or  less 
concentric  layers.  In  the  human  ovary  bundles  of 
fibrous  tissue  are  also  met  with. 

The  spindle-shaped  cells  are  most  probably  a 
young  state  of  connective  tissue. 

Between  these  bundles  of  spindle-shaped  cells 
occur  cylindrical  or  irregular  streaks  or  groups  of 
polyhedral  cells,  each  with  a  spherical  nucleus ;  they 
correspond  to  the  interstitial  epithelial  cells  men- 
tioned in  the  testis,  and  they  are  also  derived  from 
the  foetal  Wolffian  body. 

344.  According  to  the  distribution  of  the  Graafian 
follicles,  the  following  layers  can  be  distinguished  in 
the  ovary : — 

(a)  The  albuginea.  This  is  the  most  peripheral 
layer  not  containing  any  Graafian  follicles.  It  is 
composed  of  the  bundles  of  spindle-shaped  cells,  inti- 
mately interwoven.  In  man,  an  outer  and  .inner 
longitudinal,  and  a  middle  circular,  layer  can  be  made 
out  (Henle).  In  some  mammals  an  outer  longitudinal, 
an  inner  circular,  or  slightly  oblique  layer  can  be 
distinguished  in  the  albuginea. 

The  free  surface  of  the  albuginea  is  covered  with 
a  single  layer  of  polyhedral,  or  short  columnar  granu- 
lar-looking epithelial  cells,  the  germinal  epithelium 
(Waldeyer).  This  epithelium,  in  its  shape  and  aspect, 
forms  a  marked  contrast  to  the  transparent,  flattened, 
endothelial  plates  covering  the  ligamentum  latum. 

345.  (b)  The  cortical  layer  (Schron).  This  is  a 
layer  containing  the  smallest  Graafian  follicles,  either 
aggregated  as  a  more  or  less  continuous  layer  (cat  and 
rabbit),  or  in  small  groups  (human),  separated  by  the 


chap,  xxxii.]  Female  Genital  Organs. 


259 


stroma.  These  follicles  are  spherical  or  slightly  oval, 
of  about  yoV  0  nich  m  diameter,  and  each  of  them  is  limi- 
ted by  a  delicate  membrana  propria.  Inside  of  this  is 
a  layer  of  flattened,  transparent,  ej)ithelial  cells,  each 
with  an  oval,  flattened  nucleus ;  this  is  the  mem- 
brana granulosa.  The  space  within  the  follicle  is 
occupied  by,  and  filled  up  with,  a  spherical  cell — the 
ovum  cell,  or  ovum.  This  is  composed  of  a  granular- 
looking  protoplasm,  and  in  this  is  a  big  spherical,  or 
slightly  oval,  nucleus — the  germinal  vesicle.  The 
substance  of  this  is  either  a  fine  reticulum ;  limited 
by  a  delicate  membrane,  with  one  or  more  nucleoli 
or  germinal  spots,  or  it  is  in  one  of  the  phases  of 
indirect  division  or  karyokinesis,  thus  indicating 
division  of  the  ovum. 

346.  (c)  From  this  cortical  layer  to  the  zona 
vasculosa  we  find  embedded  in  the  stroma  isolated 
Graafian  follicles,  of  various  sizes,  increasing  from  the 
former  to  the  latter.  The  biggest 
follicles  measure  in  diameter  about 
—  inch.  Those  of  the  middle  layers 
are  of  medium  size  (Fig.  142).  In  them 
we  find  inside  the  membrana  propria 
the  membrana  granulosa,  made  up  of  a 
single  layer  of  transparent,  columnar, 
epithelial  cells.  The  ovum,  larger  than 
in  the  small  cortical  follicles,  fills  out 
the  cavity  of  the  follicle,  and  is 
limited  by  a  thin  hyaline  cuticle — the 
zona  pellucida.  This  appears  as  an 
excretion  of  the  cells  of  the  membrana 
granulosa.  The  protoplasm  of  the 
ovum  is  fibrillated.  The  part  sur- 
rounding the  germinal  vesicle  is  more 
transparent,  and  stains  differently  in  osmic  acid  than 
the  peripheral  part.  The  big  nucleus,  or  germinal 
vesicle,  is  limited  by  a  distinct  membrane,  and  inside 


Fig.  142. —  A  Small 
Gi-aafiau  follicle, 
from  tlie  Ovary  of 
Cat. 

The  follicle  is  lined 
wi  tli  a  layer  of  colum- 
nar epithelial  cells — 
the  membrana  granu- 
losa. The  ovum  fills 
out  the  cavity  of  the 
follicle;  it  is  sur- 
rounded by  a  thin 
zona  pellucida,  and  it 
includes  a  germinal 
vesicle  or  nucleus 
with  the  intranuclear 
reticulum.    ( Atlas. ) 


260 


Elements  of  Histology.    [Chap.  xxxn. 


this  membrane  is  a  reticulum  with  generally  one  big 
nucleolus  or  germinal  spot. 

Between  these  medium-sized  follicles  and  the 
small  follicles  of  the  cortical  layer  we  find  all  inter- 
mediate degrees  as  regards  size  of  the  follicle  and  the 
ovum,  and  especially  as  regards  the  shape  of  the  cells 
of  the  membrana  granulosa,  the  intermediate  sizes  of 

follicles  being 
lined  by  a  gran- 
ulosa made  up 
of  a  layer  of 
polyhedral  epi- 
thelial cells. 

347.  The 
deeper  Graafian 
follicles,  i.e., 
those  that  are 
to  be  regarded 
as  big  follicles, 
contain  an 
o  v  u  m — o  c  c  a  - 
sionally,  two  or 
even  three  ova 
— which  is  simi- 
lar to  that  of 
the  previous  fol- 
licles, except 
that  it  is  larger, 
and  its  zona  pel- 
lucida  thicker.  The  ovum  does  not  fill  out  the  whole 
cavity  of  the  follicle,  since  at  one  side,  between  it  and 
the  membrana  granulosa,  there  is  an  albuminous  fluid, 
the  rudiment  of  the  liquor  folliculi. 

348.  The  biggest  or  most  advanced  follicles  are  of 
great  size,  easily  visible  by  the  naked  eye,  and  con- 
tain a  large  quantity  of  this  liquor  folliculi  (Fig.  143). 
In  fact,  the  ovum  occupies  only  a  small  part  of  the 


Fig. 


large    Graafian  v 
Ovary  of  Cat. 


the 


The  follicle  is  limited  by  a  capsule,  the  theca  folliculi ; 
the  membrana  granulosa  is  composed  of  several 
layers  of  epithelial  cells.  The  ovum  with  its  distinct 
hyaline  zona  pellucida  is  embedded  in  the  epithelial 
cells  of  the  discus  proligerus.  The  cavity  of  the 
follicle  is  filled  with  fluid,  the  liquor  folliculi. 


chap,  xxxii.]   Female  Genital  Organs.  261 

cavity  of  the  follicle.  The  ovum  is  big,  surrounded  by 
a  thick  zona  pellucida,  is  situated  at  one  side,  sur 
rounded  by  the  discus  proligerus.  This  consists  of 
layers  of  polyhedral  cells,  except  the  cells  immediately 
around  the  zona  pellucida,  which  are  columnar.  The 
ovum  with  its  discus  proligerus  is  connected  with  the 
membrana  granulosa.  This  latter  consists  of  stratified 
pavement  epithelium  forming  the  entire  lining  of  the 
follicle.  The  outermost  layer  of  cells  is  columnar. 
The  membrana  propria  of  these  big  follicles  is  strength- 
ened by  concentric  layers  of  the  stroma  cells,  and  this 
represents  the  tunica  fibrosa  (Henle)  or  outer  coat  of 
the  follicle — theca  folliculi  externa.  Numerous  blood 
capillaries  connected  into  a  network  surround  the  big 
follicles. 

In  those  follicles  that  contain  a  greater  or  smaller 
amount  of  the  liquor  folliculi,  we  notice  in  the  fluid  a 
variable  number  of  detached  granulosa  cells  in  various 
stages  of  vacuolation,  maceration,  and  disintegration. 

349.  In  connection  with  the  medium-sized  and 
large  Graafian  follicles  are  seen  occasionally  smaller 
or  larger  solid  cylindrical  or  irregularly-shaped  out- 
growths of  the  membrana  granulosa  and  membrana 
propria  ;  they  indicate  a  new  formation  of  Graafian 
follicles,  some  containing  a  new  ovum.  When  these 
side  branches  become  by  active  growth  converted  into 
larger  follicles,  they  may  remain  in  continuity  with  the 
parent  follicle,  or  may  be  constricted  off  altogether. 
In  the  first  case,  we  have  one  large  follicle  with  two 
or  three  ova,  according  as  a  parent  follicle  has  given 
origin  to  one  or  two  new  outgrowths. 

Amongst  the  epithelial  cells  constituting  the  strati- 
fied membrana  granulosa  of  the  ripe  follicles  we  notice 
a  nucleated  reticulum. 

Many  follicles  reach  ripeness,  as  far  as  size  and 
constituent  elements  are  concerned,  long  before 
puberty,  and  they  are  subject  to  degeneration ;  but 


262  Elements  of  Histology.    [Chap,  xxxii. 

this  process  of  degeneration  involves  also  follicles  of 
smaller  sizes. 

350.  Before  menstruation,  generally  one,  occasion- 
ally two  or  more,  of  the  ripe  follicles  become  very 
hypersemic.  They  grow,  in  consequence,  very  rapidly 
in  size  ;  their  liquor  folliculi  increases  to  such  a  degree 
that  they  reach  the  surface  of  the  ovary  ;  finally — 
i.e.,  during  menstruation — they  burst  at  a  superficial 
point ;  the  ovum,  with  its  discus  proligerus,  is  ejected, 
and  brought  into  the  abdominal  ostium  of  the  oviduct. 
The  cavity  of  the  follicle  collapses,  and  a  certain 
amount  of  blood,  derived  from  the  broken  capillaries 
of  the  wall  of  the  follicle,  is  effused  into  it.  The  follicle 
is  converted  into  a  corpus  luteum,  by  an  active  multi- 
plication of  the  cells  of  the  granulosa.  New  capilla- 
ries with  connective  tissue  cells  derived  from  the  theca 
folliculi  externa  gradually  grow  into  the  interior,  i.e., 
between  the  cells  of  the  granulosa.  This  growth 
gradually  fills  the  follicle,  except  the  centre;  this 
contains  blood-pigment  in  the  shape  of  granules, 
chiefly  contained  in  large  cells,  and  a  few  new 
blood-vessels,  the  blood-pigment  being  the  remains 
of  the  original  blood  effused  into  the  follicle. 
But,  ultimately,  the  pigment  all  disappears,  and  a 
sort  of  gelatinous  tissue  occupies  the  centre,  while 
the  periphery — i.e.,  the  greater  part  of  the  follicle 
— is  made  up  of  the  hypertrophied  granulosa,  with 
young  capillary  vessels  between  its  cells.  The 
granulosa  cells  undergo  fatty  degeneration,  becoming 
tilled  with  several  small  fat  globules,  which  gradually 
become  confluent  into  a  big  globule.  In  this  state  the 
corpus  luteum  is  complete,  and  has  reached  the  height 
of  its  progressive  growth.  The  tissue  is  then  gradually 
absorbed,  and  cicatrical  tissue  is  left.  When  this 
shrinks  it  produces  a  shrinking  of  the  corpus  luteum. 
This  represents  the  last  stage  in  the  life  of  a 
Graafian   follicle.     The   corpus   luteum   of    Graafian 


Chap,  xxxii.]  Female  Genital  Organs.  263 

follicles,  of  which  the  ovum  has  been  impregnated, 
grows  to  a  much  larger  size  than  under  other  condi- 
tions, the  granulosa  becoming  by  overgrowth  much 
folded. 

351.  Development  of  the  ovary  and  Graa- 
fian follicles. — The  germinal  epithelium  of  the 
surface  of  the  fcetal  ovary  at  an  early  stage  undergoes 
rapid  multiplication,  in  consequence  of  which  the  epi- 
thelium becomes  greatly  thickened.  The  vascular 
stroma  of  the  ovary  at  the  same  time  increases,  and 
permeates  the  thickened  germinal  epithelium.  The 
two  tissues  in  fact  undergo  mutual  ingrowth,  as  is  the 
case  in  the  development  of  all  glands — viz.,  the  epithe- 
lial or  glandular  part  suffers  mutual  ingrowth  with 
the  vascular  connective  tissue  stroma. 

In  the  case  of  the  ovary,  larger  and  smaller 
islands  or  nests  (Balfour)  of  epithelial  cells  are  thus 
gradually  differentiated  off  from  the  superficial  epithe- 
lium. These  nests  are  largest  in  the  depth,  and  smallest 
near  the  surface.  They  remain  in  connection  with 
one  another  and  with  the  surface  for  a  considerable 
period.  Even  some  time  after  birth  some  of  the 
superficial  nests  are  still  connected  with  the  surface 
epithelium,  and  with  one  another  (Fig.  143a).  These 
correspond  to  the  ovarial  tubes  (Pnuger).  While  in 
the  rabbit  these  nests  are  solid  collections,  in  the  dog 
they  soon  assume  the  character  of  tubular  structures 
(Pnuger,  Schafer).  The  cells  constituting  the  nests 
undergo  multiplication  (by  karyokinesis),  in  conse- 
quence of  which  the  nests  increase  in  size,  and  even 
new  nests  may  be  constricted  off  from  old  ones  (see 
also  above). 

352.  At  the  earliest  stages  we  notice  in  the 
germinal  epithelium  some  of  the  cells  becoming  en- 
larged in  their  cell-body,  and  especially  their  nu- 
cleus ;  these  represent  the  primitive  ova.  When  the 
germinal  epithelium  undergoes  the  thickening  above 


264 


Elements  of  Histology.    [Chap.  xxxn. 


mentioned,  and  when  this  thickened  epithelium  sepa- 
rates into  the  nests  and  ovarial  tubes,  there  is  a 
continued  formation  of  primitive  ova — i.e.,  cells  of 
the  nests  undergo  the  enlargement  of  cell-body  and 


Fig.  143a.— From  a  Vertical  Section  through  the  Ovary  of  a 
new-born  Child. 

a,  Germinal  epithelium;  b,  ovarian  tube;  c,  primitive  ova;  d,  longer  tubes  be- 
coming constricted  off  into  several  Graafian  follicles ;  e,  larte  nests ;  f, 
isolated  finished  Graafian  follicles;  g,  blood-vessels.  (Waldeyer,  in  Strieker's 
Manual.) 


nucleus,  by  which  they  are  converted  into  primitive 
ova.  Like  the  other  epithelial  cells,  the  primitive 
ova  of  the  nests  and  ovarial  tubes  undergo  division 
into  two  or  even  more  primitive  ova  after  the  mode 
of  karyokinesis  (Balfour).  Thus  each  nest  contains 
a  series  of  ova. 

353.  The  ordinary  small  epithelial  cells  of  the 
nests  and  ovarial  tubes  serve  to  form  the  membrana 
granulosa  of   the    Graafian   follicles.      According   to 


chap,  xxxii.]   Female  Genital  Organs.  265 

the  number  of  ova  in  a  nest  or  in  an  ovarial  tube 
a  subdivision  takes  place  in  so  many  Graafian  follicles, 
each  consisting  of  one  ovum  with  a  more  or  less 
complete  investment  of  small  epithelial  cells — i.e.,  a 
membrana  granulosa.  This  subdivision  is  brought 
about  by  the  ingrowth  of  the  stroma  into  the  nests. 

The  superficial  nests  being  the  smallest,  as  above 
stated,  form  the  cortical  layer  of  the  small  Graafian 
follicles  ;  the  deeper  ones  give  origin  to  larger  follicles. 
Thus  we  see  that  the  ovum  and  the  cells  of  the 
membrana  granulosa  are  derived  from  the  primary 
germinal  epithelium ;  all  other  parts — membrana 
propria,  theca  externa,  stroma,  and  vessels — are 
derived  from  the  foetal  stroma. 

There  is  a  good  deal  of  evidence  to  show  that 
ova  and  Graafian  follicles  are,  as  a  rule,  reproduced 
after  birth  (Pfliiger,  Kolliker),  although  other  ob- 
servers (Bischoff,  Waldeyer)  hold  the  opposite  view. 

354.  (2)  The  oviduct. — The  oviduct  consists  of 
a  lining  epithelium,  a  mucous  membrane,  a  muscular 
coat,  and  an  outer  fibrous  coat — the  serous  covering, 
or  peritoneum.  The  epithelium  is  columnar  and 
ciliated.  The  mucous  membrane  is  much  folded  ;  it 
is  a  connective  tissue  membrane  with  networks  of 
capillary  blood-vessels.  In  man  and  mammals  there 
are  no  proper  glands  present,  although  there  are  seen 
appearances  in  sections  which  seem  to  indicate  the 
existence  of  short  gland  tubes ;  but  these  appear- 
ances are  explained  by  the  folds  of  the  mucous 
membrane.  The  muscular  coat  is  composed  of  non- 
striped  muscular  tissue  of  a  pre-eminently  circular 
arrangement ;  in  the  outer  part  there  are  a  few 
oblique  and  longitudinal  bundles.  The  serous  cover- 
ing contains  numerous  elastic  fibrils  in  a  connective 
tissue  matrix. 

355.  (3)  The  uterus. — The  epithelium  lining 
the  cavity  of  the  uterus  is  a  single  layer  of  columnar 


266  Elements  of  Histology.    [Chap.xxxn. 

cells,  each  with  a  bundle  of  cilia  on  their  free  surface. 
These  are  very  easily  detached,  and  therefore  difficult 
to  find  in  a  hardened  and  preserved  specimen.  But 
in  the  fresh  and  well-preserved  human  uterus  (Fried- 
lander),  as  well  as  in  that  of  mammals,  the  cel]s  are 
distinctly  ciliated.  The  whole  canal  of  the  cervix  is 
also  lined  with  ciliated  epithelium,  but  in  children, 
according  to  Lott,  only  beginning  from  the  middle. 
The  surface  of  the  portio  vaginalis  uteri  is,  like  that 
of  the  vagina,  covered  with  stratified  pavement  epithe- 
lium. 

356.  The  mucous  membrane  of  the  cervix  is 
different  from  that  of  the  fundus.  In  the  former  it  is 
a  fibrous  tissue  possessed  of  permanent  folds — the 
palmse  plicatse.  Few  thin  bundles  of  non-striped  mus- 
cular tissue  penetrate  from  the  outer  muscular  coat 
into  the  mucous  membrane.  Between  the  palmse 
plicate  are  the  openings  of  minute  gland-tubes,  more 
or  less  cylindrical  in  shape.  They  possess  a  mem- 
brana  propria  and  a  distinct  lumen  lined  with  a  single 
layer  of  columnar  epithelial  cells,  which,  according 
to  some,  are  ciliated  in  the  new-born  child,  but,  ac- 
cording to  Friedlander,  non-ciliated.  Goblet-cells  are 
met  with  amongst  the  lining  epithelium.  Several 
observers  (Kolliker,  Hennig,  Tyler  Smith,  and  others) 
maintain  the  existence  of  minute,  thin,  and  long 
vascular  papilla  projecting  above  the  general  surface 
of  the  mucous  membrane  in  the  lower  part  of  the 
cervix  ;  these  apparent  papillae  are,  however,  only  due 
to  sections  through  the  folds  of  the  mucous  membrane. 
The  mucous  membrane  of  the  fundus  is  a  spongy 
plexus  of  fine  bundles  of  fibrous  tissue,  covered  or 
lined  respectively  with  numerous  small  endothelial 
plates,  each  with  an  oval  flattened  nucleus.  The 
spaces  of  this  spongy  substance  are  lymph-spaces,  and 
contain  the  glands  and  the  blood-vessels  (Leopold). 

357.  The    glands  —  glandulee  utcrinse  —  are 


chap,  xxxn.]  Female  Genital  Organs.  267 

short  tubular  glands.  They  occur  in  the  new-born 
child  chiefly  at  the  sides  ;  during  puberty  their  number 
and  their  size  increase  considerably,  new  glands  being 
formed  by  the  ingrowth  of  the  surface  epithelium  into 
the  mucous  membrane  (Kundrat  and  Engelmann). 
During  menstruation,  and  especially  during  pregnancy, 
they  greatly  increase  in  length.  They  are  more  or 
less  wavy  and  branched  at  the  bottom.  A  delicate 
membrana  propria  forms  the  boundary  of  the  tube ;  a 
distinct  lumen  is  seen  in  the  middle,  and  this  is  lined 
with  a  single  layer  of  ciliated  columnar  epithelium 
(Allen  Thomson,  Nylander,  Friedlander,  and  others). 

358.  During  menstruation  the  thickness  of  the 
mucous  membrane  increases,  the  epithelium  of  the 
surface  and  of  the  greater  part  of  the  glands  being- 
destroyed  by  fatty  degeneration,  and  finally  alto- 
gether detached.  Afterwards  its  restitution  takes 
place  from  the  remnant  in  the  depth  of  the  glands. 
But  according  to  J.  Williams  and  also  Wyder,  the 
greater  part  of  the  mucous  membrane,  in  addition  to 
the  epithelium,  is  destroyed  during  menstruation. 

The  muscular  coat  forms  the  thickest  part  of  the 
wall  of  the  uterus  ;  it  is  composed  entirely  of  the  non- 
striped  variety. 

In  the  cornua  uteri  of  mammals  the  muscular 
coat  is  generally  composed  of  an  inner  thicker  circular 
and  an  outer  thinner  longitudinal  stratum,  a  few 
oblique  bundles  passing  from  the  latter  into  the 
former.  In  the  human  uterus  the  muscular  coat  is 
composed  of  an  outer  thin  longitudinal,  a  middle 
thick  layer  of  circular  bundles,  and  an  inner  thick 
one  of  oblique  and  circular  bundles.  Within  these 
layers  the  bundles  form  plexuses. 

359.  The  arterioles  in  the  cervix  and  their  capil- 
laries are  distinguished  by  the  great  thickness  of  their 
wall.  The  mucous  membrane  contains  the  capillary 
networks.      These    discharge   their   blood   into   veins 


268  Elements  of  Histology.    [Chap,  xxxii. 

situated  in  the  muscular  coat.  There  the  veins  are 
very  numerous,  and  arranged  in  dense  plexuses,  those  of 
the  outer  and  inner  stratum  being  smaller  than  those 
of  the  middle  stratum,  where  they  correspond  to  huge 
irregular  sinuses,  the  bundles  of  muscular  tissue  of 
the  muscular  coat  giving  special  support  to  these 
sinuses.  Hence  the  plexus  of  venous  sinuses  of  the 
middle  stratum  represents  a  sort  of  cavernous  tissue. 

360.  The  lymphatics  are  very  numerous;  in 
the  intermuscular  connective  tissue  of  the  muscular 
coat  are  lymph  sinuses  and  lymph  clefts  forming  an 
intercommunicating  system  ;  they  take  up  the  lymph 
sinuses  of  the  mucous  membrane  above  mentioned, 
and  on  the  other  hand  lead  into  a  plexus  of  lymphatic 
vessels  with  valves,  situated  in  the  subserous  connec- 
tive tissue. 

The  nerves  entering  the  mucous  membrane  are 
connected  with  ganglia.  According  to  Lindgren,  there 
is  in  the  mucous  membrane  a  plexus  of  non-medu Hated 
nerve-fibres,  which,  near  the  epithelium,  break  up 
into  their  constituent  primitive  fibrillse. 

361.  (4)  The  vagina. — The  epithelium  lining 
the  mucous  membrane  is  a  thick,  stratified,  pavement 
epithelium.  The  superficial  part  of  the  mucous  mem- 
brane— i.e.,  the  mucosa — is  a  dense,  fibrous,  connective 
tissue  with  numerous  networks  of  elastic  fibres;  it 
projects  into  the  epithelium  in  the  shape  of  numerous 
long,  single  or  divided  papillae,  each  with  a  simple  or 
complex  loop  of  capillary  blood-vessels.  The  mucosa 
with  the  covering  epithelium  projects  above  the  gene- 
ral surface  in  the  shape  of  longer  or  shorter,  conical 
or  irregular,  pointed  or  blunt,  permanent  folds — the 
rugse.  These  contain  a  plexus  of  large  veins,  between 
which  are  bundles  of  non-striped  muscular  tissue ; 
hence  they  resemble  a  sort  of  cavernous  tissue. 

Outside  of  the  mucosa  is  the  loose  submucosa 
containing  a  second  venous  plexus ;   its   meshes  are 


chap,  xxxii.]  Female  Genital  Organs.  269 

elongated  and  parallel  to  the  long  axis  of  the  vagina. 
Outside  of  the  submucous  tissue  is  the  muscular  coat, 
consisting  of  an  inner  circular  and  an  outer  longitu- 
dinal stratum  of  non-striped  muscular  tissue.  Oblique 
bundles  pass  from  one  stratum  into  the  other.  From 
the  circular  stratum  bundles  may  be  traced  into  the 
submucosa  and  mucosa.  A  layer  of  fibrous  tissue 
forms  the  outer  boundary  of  the  wall  of  the  vagina, 
and  in  it  is  the  most  conspicuous  plexus  of  veins,  the 
plexus  venosus  vaginalis.  This  plexus  also  contains 
bundles  of  non-striped  muscular  tissue,  and  therefore 
resembles  a  cavernous  tissue  (Gussenbaur.)  It  is 
not  quite  definitely  ascertained  whether  or  not  there  are 
secreting  glands  in  the  mucous  membrane  of  the 
vagina.  Von  Preuschen  and  also  Hennig  described 
tubular  glands  in  the  upper  part  of  the  fornix  and  in 
the  introitus. 

The  lymphatics  form  plexuses  in  the  mucosa,  sub- 
mucosa, and  the  muscular  coat.  The  first  are  small 
vessels,  the  second  are  larger  than  the  third  and  possess 
valves.  The  efferent  vessels  form  a  rich  plexus  of 
large  trunks  with  saccular  dilatations  in  the  outer 
fibrous  coat. 

There  are  in  the  mucous  membrane  solitary  lymph 
follicles  and  diffuse  adenoid  tissue  (Loevenstein). 

Numerous  ganglia  are  contained  in  the  nerve 
plexus  belonging  to  the  muscular  coat. 

End  bulbs  in  connection  with  the  nerve-fibres  of 
the  mucosa  have  been  mentioned  in  Chapter  XY. 

362.  (5)  The  urethra — The  structure  of  the 
female  urethra  is  similar  to  that  of  the  male,  except 
that  the  lining  epithelium  is  a  sort  of  stratified  tran- 
sitional epithelium,  the  superficial  cells  being  short, 
columnar,  or  club-shaped ;  underneath  this  layer  are 
several  layers  of  polyhedral,  or  cubical  cells.  Near 
the  orificium  externum  the  epithelium  is  stratified 
pavement  epithelium. 


270  Elements  of  Histology.  [Chap,  xxxiii. 

The  muscular  coat  is  composed  of  an  inner* longi- 
tudinal, and  an  outer  circular,  layer  of  non-striped 
muscular  tissue. 

363.    (6)   The   nymphse,  clitoris,   and   vesti- 

bulum. — These  are  lined  with  thick  stratified  epi- 
thelium, underneath  is  a  fibrous  connective  tissue 
mucous  membrane,  extending  into  the  epithelium  in 
the  shape  of  cylindrical  papillae  with  capillary  loops 
and  nerve-endings  (end  bulbs).  The  nymphee  contain 
large  sebaceous  follicles,  but  no  hairs. 

The  nymphse  contain  a  plexus  of  large  veins  with 
bundles  of  non-striped  muscular  tissue;  hence  it  re- 
sembles a  cavernous  tissue  (Gassenbaur).  The  corpora 
cavernosa  of  the  clitoris,  the  glans  clitoridis,  and  the 
bulbi  vestibuli,  correspond  to  the  analogous  parts  in 
the  penis  of  the  male.  The  glands  of  Bartholin  corre- 
spond in  structure  to  the  glands  of  Cowper  in  the 
male. 


CHAPTER    XXXIII. 

THE  MAMMARY  GLAND. 

364.  This,  like  other  glands,  consists  of  a  frame- 
work and  parenchyma.  The  former  is  lamellar  fibrous 
connective  tissue  subdividing  the  latter  into  lobes  and 
lobules  and  containing  a  certain  amount  of  elastic 
fibres.  In  some  animals  (rabbit,  guinea-pig)  there  are 
also  small  bundles  of  non-striped  muscular  tissue. 
From  the  interlobular  septa  fine  bundles  of  fibrous 
tissue  with  branched  connective  tissue  corpuscles  pass 
between  the  alveoli  of  the  gland  substance.  The 
amount  of  this  interalveolar  tissue  varies  in  different 
places,  but  in  the  active  gland  is  always  relatively 
scanty. 


Chap,  xxxiii.]    The  Mammary  Glaxd.  271 

Migratory  or  lymph  corpuscles  are  to  be  met  with 
in  the  i literal veolar  connective  tissue  of  both  active 
and  resting  glands.  In  the  latter  they  are  more 
numerous  than  in  the  former.  According  to  Creighton, 
they  are  derived,  in  the  resting  gland,  from  the  epi- 
thelium of  the  gland  alveoli.  Granular  large  yellow 
(pigmented)  nucleated  cells  occur  in  the  connec- 
tive tissue,  and  also  in  the  alveoli  of  the  resting 
gland,  and  Creighton  considers  them  both  identical, 
and  derived  frorn  the  alveolar  epithelium.  And 
according  to  this  author,  the  production  of  these  cells, 
would  .constitute  the  principal  function  of  the  resting 
gland. 

The  large  ducts  as  they  pass  from  the  gland  to 
the  nipple,  acquire  a  thick  sheath,  containing  bundles 
of  non-striped  muscular  tissue.  These  latter  are  de- 
rived from  the  bundles  of  non-striped  muscular  tissue 
present  in  the  skin  of  the  nipple  of  the  breast. 

The  small  ducts  in  the  lobules  of  the  gland  tissue 
possess  a  membrana  propria,  and  a  lining — a  single 
layer  of  longer  or  shorter  columnar  epithelial  cells. 

The  terminal  branches  of  the  ducts,  i.e.,  just  before 
these  latter  pass  into  the  alveoli,  are  lined  with  a 
single  layer  of  flattened  pavement  epithelium  cells ; 
they  are  analogous  to  the  intermediary  portion  of  the 
ducts  of  the  salivary  glands  (see  Chap.  XXII.). 

365.  Each  of  these  terminal  branches  divides  and 
takes  up  several  alveoli  (Fig.  144).  These  are  wavy 
tubes,  saccular  or  flask-shaped.  The  alveoli  are 
larger  in  diameter  than  the  intralobular  ducts.  Each 
alveolus  in  the  active  gland  has  a  relatively  large 
cavity,  varying  in  different  alveoli ;  it  is  lined  with  a 
single  layer  of  polyhedral,  granular-looking,  or  short 
columnar  epithelial  cells,  each  with  a  spherical  nucleus  \ 
a  membrana  propria  forms  the  outer  limit.  This  mem- 
brana propria,  like  that  of  the  salivary,  lachrymal  and 
other  glands,  is  a  basket-work  of  branched  cells. 


272 


Elements  of  Histology.  [Chap,  xxxiii. 


In  the  active  gland  each  epithelial  cell  is  capable 
of  forming  in  its  interior  one  or  more  smaller  or  larger 
oil  globules.  These  may,  and  generally  do,  become 
confluent,  and,  pressing  the  nucleus  towards  one  side 
of  the  cell,  give  to  the  latter  the  resemblance  of  a  fat- 
cell.  The  oil  globules  are  finally  ejected  by  the  cell- 
protoplasm  into  the  lumen  of  the  alveolus,  and  repre- 


Fig.  144.—  From  a  Section  through  the  Mammary  Gland  of  Cat  in  a 
late  stage  of  Pregnancy. 

a,  The  epithelial  cells  lining  the  gland-alveoli,  seen  in  profile ;  6,  the  same,  seen 
from  the  surface.  Many  epithelial  cells  contain  an  oil  globule.  In  the  cavity 
of  some  of  the  alveoli  are  milk  globules  and  granular  matter.  (Atlas.) 


sent  now  the  milk  globules.  The  cell  resumes  its 
former  solid  character,  and  commences  again  to  form 
oil  globules  in  its  protoplasm.  The  epithelial  cells, 
as  long  as  the  secretion  of  milk  lasts,  go  on  again 
and  again  forming  oil  globules  in  the  above  manner 
without  being  themselves  destroyed  (Langer).  These 
milk  globules,  when  in  the  lumen  of  the  alveoli,  are 


chap,  xxxiii.]    The  Mammary  Gland.  273 

enveloped  in  a  delicate  cuticle — the  albumin  mem- 
brane of  Ascherson.  This  membrane  they  receive 
from  the  cell  protoplasm. 

According  to  the  state  of  secretion,  most  epithelial 
cells  lining  an  alveolus  may  be  in  the  condition  of 
forming  oil  globules,  or  only  some  of  them ;  and 
according  to  the  rate  in  which  milk  globules  are  formed 
and  carried  away,  the  alveoli  differ  in  the  number  of 
milk  globules  they  contain. 

According  to  Schmid,  the  epithelial  cells,  after 
having  secreted  milk  globules  for  some  time,  finally 
break  up,  and  are  replaced  by  new  epithelial  cells 
derived  by  the  division  of  the  other  still  active 
epithelial  cells. 

366.  The  resting  gland,  i.e.,  the  gland  of  a  non- 
pregnant or  non-suckling  individual,  contains,  compara- 
tively speaking,  few  alveoli,  but  a  great  deal  of  fibrous 
connective  tissue ;  the  alveoli  are  all  solid  cylinders, 
containing  within  the  limiting  membrana  propria 
masses  of  polyhedral  granular-looking  epithelial  cells. 
During  pregnancy  these  solid  alveoli  undergo  rapid 
multiplication,  elongation,  and  thickening,  owing  to 
the  rapid  division  of  the  epithelial  cells. 

Finally,  when  milk  secretion  commences,  the  cells 
occupying  the  central  part  of  the  alveolus  undergo  the 
fatty  degeneration  just  like  the  peripheral  cells,  but 
they,  i.e.,  the  central  cells,  are  eliminated,  while  the 
peripheral  ones  remain.  These  central  cells  are  the 
colostrum  corpuscles,  and  consequently  they  are  found 
in  the  milk  of  the  first  few  days  only. 

367.  Ordinary  milk  contains  no  colostrum  corpus- 
cles, but  only  milk  globules  of  many  various  sizes,  from 
the  size  of  a  granule  to  that  of  a  globule  several  times 
as  big  as  an  epithelial  cell  of  an  alveolus  of  the  milk 
gland.  These  large  drops  are  produced  by  fusion  of 
small  globules  after  having  passed  out  of  the  alveoli. 
Each  milk  globule  is   an   oil  globule   surrounded,   as 

s 


274  Elements  of  Histology.  [Chap,  xxxiv. 

stated  above,  by  a  thin  albuminous  envelope — Ascher- 
son's  membrane.  The  small  bits  of  granular  substance 
met  with  here  and  there,  are  probably  the  remains  of 
broken-down  protoplasm  of  epithelial  cells. 

368.  Each  gland  alveolus  is  surrounded  by  a  dense 
network  of  capillary  blood-vessels.  The  alveoli  are 
surrounded  by  lymph  spaces  like  those  in  the  salivary 
glands  (Coyne)  and  these  spaces  lead  into  networks  of 
lymphatic  vessels  of  the  interlobular  connective  tissue. 


CHAPTER  XXXIV. 

THE    SKIN". 

369.  The   skin   consists  of  the   following   layers' 
(Fig.   145)  : — (1)  the  epidermis;    (2)  the   corium,  or 
cutis  vera,   with   the   papillae;   (3)  the    subcutaneous 
tissue,  with  the  adipose  layer  or  the  adipose  tissue. 

370.  (1)  The  epidermis  (Fig.  14),  in  all  its 
constituent  elements,  has  been  minutely  described  in 
Chapter  III.  Its  thickness  varies  in  different  parts, 
and  is  chiefly  dependent  on  the  variable  thickness  of 
the  stratum  corneum.  This  is  of  great  thickness  in 
the  palm  of  the  hand  and  the  sole  of  the  foot.  The 
stratum  Malpighii  fits  into  the  depressions  between 
the  papillse  of  the  corium  as  the  interpapillary  pro- 
cesses. The  presence  of  prickle  cells,  of  pigment 
granules,  and  of  branched  interstitial  nucleated  cells, 
&c,  has  been  mentioned  in  Chapter  III. 

There  occur  in  the  stratum  Malpighii  migratory 
cells  of  granular  aspect;  they  appear  to  migrate  from 
the  papillary  layer  of  the  corium  into  the  stratum 
Malpighii  (Biesiadecki). 

371.  (2)  The  corium  is  a  dense  feltwork  of 
bundles   of    fibrous   connective   tissue,   with    a    large 


Chap.  XXXIV.] 


The  Skin. 


275 


admixture  of  networks  of  elastic  fibres.  From  the 
surface  of  the  coriura  project  small  conical  or  cylin- 
drical papillce.  These  are  best  developed  in  those 
parts  where  the  skin  is  thick,  e.g.,  volar  side  of 
hand  and  foot,  scalp,  lips  of  mouth,  &c.  Between 
the  surface  of  the  corium  and  the  epidermis  there 
is  a  basement  membrane.     Migratory  cells,  with  and 


Fig.  145.— Vertical  Section  through  the  Skin  of  Human  Finger. 

a,  Stratum  corneura  ;  5,  stratum  lucidum:  c,  stratum  Malpighii :  d,  Meissner's, 
or  tactile  corpuscles ;  e,  blood-vessels  cut  across ;  /,  a  sudoriferous  canal  or 
duct. 

without  pigment  granules  in  their  interior,  are  met 
with,  especially  in  the  superficial  part  of  the  corium ; 
they,  as  well  as  the  fixed  or  branched  connective 
tissue  corpuscles  (see  par.  40),  and  other  structures,  as 
vessels  and  nerves,  lie  in  the  interfascicular  spaces. 

372.  (3)  The  superficial  part  of  the  subcuta- 
neous tissue  insensibly  merges  into  the  deep  part  of 
the  corium  ;  it  consists  of  bundles  of  fibrous  connective 
tissue  aggregated  into  trabecule  crossing  one  another 


276  Elements  %of  Histology.    [Chap,  xxxiv. 

and  interlacing  in  a  complex  manner.  Numerous 
elastic  fibres  are  attached  to  these  trabecule.  It  con- 
tains groups  of  fat  cells,  in  many  places  arranged  as 
more  or  less  continuous  lobules  of  fat  tissue,  forming 
the  stratum  advposum.  These  lobules  are  separated 
by  septa  of  fibrous  connective  tissue  ;  their  structure 
and  development,  and  the  distribution  of  the  blood- 
vessels amongst  the  fat  cells,  have  been  described 
in  par.  45.  The  deep  part  of  the  subcutaneous  tissue 
is  loose  in  texture,  and  contains  the  large  vascular 
trunks  and  the  big  nerve  branches. 

373.  The  superficial  part  of  the  subcutaneous 
tissue,  or,  as  some  have  it,  the  deep  part  of  the 
corium,  contains  the  sudoriparous  or  sweat  glands. 
Each  gland  is  a  single  tube  coiled  up  into  a  dense 
clump  of  about  —^  of  an  inch  in  diameter — in  some 
places,  as  in  the  axilla,  reaching  as  much  as  six  times 
this  size.  From  each  gland  a  duct — the  sudori- 
ferous canal — passes  through  the  corium  in  a  slightly 
wavy  and  vertical  direction  towards  the  epidermis ; 
it  penetrates  more  or  less  spirally  through  the  inter- 
papillary  process  of  the  stratum  Malpighii  and  the 
rest  of  the  epidermis,  and  appears  with  an  open  mouth 
on  the  free  surface  of  the  skin. 

The  total  number  of  sweat  glands  in  the  human 
skin  has  been  computed  by  Krause  to  be  over  two 
millions  ;  but  it  varies  greatly  in  different  parts  of  the 
body,  the  largest  number  occurring  in  the  palm  of 
the  hand,  the  next  in  the  sole  of  the  foot,  the  next 
on  the  dorsum  of  the  hand  and  foot,  and  the  smallest 
in  the  skin  of  the  dorsum  of  the  trunk. 

374.  The  sudoriferous  canal  and  the  coiled  tube 
possess  a  distinct  lumen ;  this  is  lined  with  a  delicate 
cuticle,  especially  marked  in  the  sudoriferous  canal 
and  in  the  commencement  of  the  coiled  tube.  In  the 
epidermis  the  lumen  bordered  by  this  cuticle  is  all 
that  is  present  of  the  sudoriferous  canal.     It  receives 


Chap.  XXXIV.] 


The  Skin. 


277 


a  continuation  from  the  middle  layer  of  the  stratum 
Malpighii  and  from  the  basement  membrane ;  the 
former  is  the  lining  epithelium,  the  latter  the  limiting 
membrana  propria  of  the  sudoriferous  canal.  The 
epithelium  consists  of  two  or  three  layers  of  small 
polyhedral  cells,  each  with  a  spherical  or  oval  nucleus. 


Fig.  146. — From  a  Section  through.  Human  Skin,  showing  the  Sweat 
gland  tuhes  cut  in  various  directions. 

a,  First  part  of  the  coiled  tube  seen  in  longitudinal  section  :  6,  the  same  seen  in 
cross  section ,  c,  the  distal  part  seen  in  longitudinal  section ;  d,  the  same  seen 
in  cross  section.    (Atlas.) 

375.  The  structure  of  the  sudoriferous  canal  is 
then — a  limiting  membrana  propria,  an  epithelium 
composed  of  two  or  three  layers  of  polyhedral  cells,  an. 
internal  delicate  membrane,  and,  finally,  the  central 
cavity,  or  lumen. 

The  first  part — about  one-third  or  one-fourth — 
of  the  coiled  tube  (Fig.  146)  is  of  the  same  struc- 
ture, and  is  directly  continuous  with  the  sudoriferous 
canal,  with  which  it  is  identical,  not  only  in  structure, 
but  in  size.  The  remainder  of  the  coiled  tube — i.e., 
the  distal  part — is   larger  in  diameter,  and  differs  in 


278  Elements  of  Histology.    [Chap,  xxxiv. 

these  essential  respects,  that  its  epithelium  is  a  single 
layer  of  transparent  columnar  cells,  and  that  there 
is  between  this  and  the  limiting  membrana  propria 
a  layer  of  non-striped  muscle  cells  (Koliiker)  arranged 
parallel  with  the  long  axis  of  the  tube.  In  some 
places,  as  in  the  palm  of  the  hand  and  foot,  in  the 
scrotum,  the  nipple  of  the  breast,  the  scalp,  but 
especially  in  the  axilla,  this  distal  portion  of  the  coiled 
tube  is  of  very  great  length  and  breadth,  and  its 
epithelial  cells  contain  a  variable  amount  of  granules. 
It  appears  to  me  that  the  cells  resemble  in  this 
respect  those  of  the  serous  salivary  glands  and  the 
chief  cells  of  the  gastric  glands  (Langley),  inasmuch 
as  they  produce  in  their  interior  larger  or  smaller 
granules  which,  are  used  up  during  secretion,  from  the 
periphery  towards  the  lumen. 

376.  The  ceruminous  glands  of  the  meatus 
auditorius  externus  are  of  the  same  structure  as  the 
distal  portion  just  described,  except  that  the  inner 
part  of  the  cell  protoplasm  of  the  epithelium  contains 
yellowish  or  brownish  pigment,  found  also  in  their 
secretion,  i.e.,  in  the  wax  of  the  ear. 

Around  the  anus  there  is  an  elliptical  zone,  in  the 
skin  of  which  are  found  large  coiled  gland  tubes — the 
circumanal  glands  of  A.  Gay — which  are  identical  in 
structure  with  the  distal  portion  of  the  sweat  gland 
tubes. 

377.  The  sweat  glands  develop  as  a  solid  cylin- 
drical outgrowth  of  the  stratum  Malpighii  of  the 
epidermis,  which  gradually  elongates  till  it  reaches 
the  superficial  part  of  the  subcutaneous  tissue,  where  it 
commences  to  coil.  The  lumen  of  the  tube  is  of 
later  appearance.  The  membrana  propria  is  derived 
from  the  tissue  of  the  cutis,  but  the  epithelium  and 
muscular  layer  are  both  derived  from  the  original 
outgrowth  of  the  epidermis. 

378.  The   hair-follicles  (Fig.    147).— The  skin 


Chap.  XXXIV.J 


The  Skin. 


279 


almost  everywhere  contains  cylindrical  follicles,  planted 
more  or  less  near  to  one  another,  and  in  groups.  In 
each  of  them  is  fixed  the  root  of  a  hair ;  that  part 


Fig.  It7.— Longitudinal  Section  through  a  Human  Hair. 

1,  Epidermis;   2,  mouth  of  hair  follicle;  3,  sebaceous  follicle;  4,  musculus 
arrector  pili ;  5,  papilla  of  hair ;  6,  adipose  tissue.    (Atlas.) 

of  the  hair  which  projects  beyond  the  general  surface 
of  the  skin  is  the  shaft. 

A  very  few  places  contain  no  hair-follicles,  such, 
for  instance,  as  the  volar  side  of  the  hand  and  foot, 
and  the  skin  of  the  penis. 

In  size,  the  hairs  and  hair-follicles  differ  in  diffe- 
rent parts.    Those  of  the  scalp,  the  cilia  of  the  eyelids, 


280  Elements  of  Histology.    [Chap,  xxxiv. 

the  hairs  of  the  axilla  and  pubic  region,  those  of 
the  male  whiskers  and  moustache,  are  coarse  and 
thick,  while  the  hairs  of  other  places — e.g.,  the  skin- 
surface  of  the  eyelids,  the  middle  of  the  arm  and 
forearm,  &c. — are  very  minute  :  but,  as  regards  struc- 
ture, they  are  all  very  much  alike. 

379.  A  complete  hair  and  hair-follicle — that  is,  the 
papillary  hair  of  Unna — shows  the  following  struc- 
ture : — 

The  hair -follicle.  Each  hair -follicle  commences 
on  the  free  surface  of  the  skin  with  a  funnel- 
shaped  opening  or  mouth;  it  passes  in  an  oblique 
direction  through  the  corium  into  the  subcutaneous 
tissue,  in  whose  middle  strata — i.e.,  in  the  stratum 
adiposum — it  terminates  with  a  slightly  enlarged 
extremity,  with  which  it  is  invaginated  over  a  rela- 
tively small  fungus-shaped  papilla.  This  latter  is  of 
fibrous  tissue,  containing  numerous  cells  and  a  loop  of 
capillary  blood-vessels. 

Minute  hairs  do  not  reach  with  their  follicles  to 
such  a  depth  as  the  large  coarse  hairs,  the-  former  not 
extending  generally  much  farther  than  the  deep  part 
of  the  corium.  Degenerating  and  imperfect  hairs 
(see  below)  also  do  not  reach  to  such  a  depth  as  the 
perfect  large  hair-follicles.  In  individuals  with 
"woolly"  hair — e.g.,  the  negro  race  (0.  Stewart),  and 
in  animals  with  "  woolly  "  hair,  such  as  the  fleece  of 
sheep — the  deep  extremity  of  the  hair-follicle  is 
curved,  sometimes  even  slightly  upwards. 

380.  The  structure  of  a  hair-follicle  is  as  follows 
(Fig.  148) :  There  is  an  outer  coat  composed  of 
fibrous  tissue ;  this  is  the  fibrous  coat  of  the  hair- 
sac.  It  is  merely  a  condensation  of  the  surround- 
ing fibrous  tissue,  and  is  continuous  with  the 
papilla  at  the  extremity  of  the  hair-follicle.  About 
the  end  of  the  hair-follicle,  or  sometimes  as  much 
as    in    the    lower    fourth,    there    is    inside    of    this 


Chap.  XXXIV.] 


The  Skin. 


281 


fibrous  layer  of  the  hair-sac  a  single  continuous 
layer  of  transversely  or  circularly-arranged  spindle- 
shaped  cells,  each  with  an  oval  flattened  or  staff- 
shaped  nucleus,  completely  resembling,  and  generally 
considered  to  be, 
non-striped  mns-  l 

cle  cells.  Inside 
of  this  layer  of 
the  hair-sac  is 
a  glassy-looking, 
hyaline,  basement 
membrane,  which  a-.U| 
is  not  very  <hs-  «~-»r||- Wgrg]5| 
tmct    m   minute  \\wk&x\$TXV'- 


hairs,  but  is  sufh- 
ciently  conspicu- 
ous in  large  adult 
hair  -  follicles. 
This  glassy  mem- 
brane, as  it  is 
called,  is  a  direct 
continuation  of 
the         basement 


Fig.  148. 


-Cross  Section  through  a  Human  Hair 
and  Hair  Follicle. 


a,  Marrow  of  hair ;  6,  cortex  of  hair ;  c,  cuticle  of 
hair;  d,  Huxley's  layer  of  inner  root -sheath; 
e,  Henle's  layer  of  inner  root-shcath ;  /,  outer  root- 
sheath  ;  g,  glassy  membrane  ;  h,  fibrous  coat  of  hair 
sac ;  i,  lymph  spaces  in  the  same. 


membrane  of  the 

surface  of  the  corium,  and  it  can  be  traced  as  a  delicate 

membrane  also  over  the  surface  of  the  hair-papilla. 

381.  Next  to  the  glassy  membrane  is  the  outer 
root-sheath,  the  most  conspicuous  part  of  the  hair-fol- 
licle. It  consists  of  a  thick  stratified  epithelium  of 
exactly  the  same  nature  as  the  stratum  Malpighii  of 
the  epidermis,  with  which  it  is  directly  continuous, 
and  from  which  it  is  developed.  In  the  outer  root- 
sheath  the  layer  of  cells  next  to  the  glassy  membrane 
is  columnar,  just  like  the  deepest  layer  of  cells  in  the 
stratum  Malpighii ;  then  follow  inwards  several  layers 
of  polyhedral  cells ;  and,  finally,  flattened  nucleated 
scales  form  the  innermost  boundary  of  the  outer  root- 


282  Elements  of  Histology.    [Chap,  xxxiv. 

sheath.  The  stratum  granulosum  of  the  stratum 
Malpighii  is  not  continued  beyond  the  mouth  of  the 
hair-follicle,  but  there  it  is  generally  very  marked. 
The  outer  root-sheath  becomes  greatly  attenuated  at 
the  papilla — in  fact,  is  there  continuous  with  the  cells 
constituting  the  hair-bulb. 

382.  The  centre  of  the  hair-follicle  is  occupied  by 
the  root  of  the  hair,  which  terminates  with  an  en- 
larged extremity — the  hair-bulb;  this  grasps  the 
whole  papilla.  The  hair-bulb  is  composed  of  poly- 
hedral epithelial  cells,  separated  from  one  another 
by  cement  substance,  and  continuous  with  the  cells 
of  the  extremity  of  the  outer  root-sheath,  from 
which  they  originate  in  the  first  instance ;  just  over 
the  papilla  there  is  a  special  row  of  short  columnar 
cells,  which  are  in  an  active  state  of  multiplication, 
and  by  which  continuously  new  cells  are#  formed. 
Thus  a  gradual  shifting  of  the  cells  of  the  hair- 
bulb  upwards  into  the  cavity  of  the  hair-follicle  — 
i.e.,  the  hair — takes  place ;  but  at  the  same  time 
these  progressing  cells  become  elongated,  spindle- 
shaped,  and  constitute  the  cells  of  the  hair  substance, 
except  in  the  very  centre,  where  they  remain  poly- 
hedral, so  as  to  represent  the  cells  of  the  marrow  of 
the  hair,  and  in  the  periphery,  where  they  remain 
more  or  less  polyhedral,  so  as  to  form  the  inner  root- 
sheath. 

383.  The  root  of  the  hair,  except  at  the  hair- 
bulb,  shows  the  following  parts  :  The  substance  of  the 
hair,  the  cuticle,  and  the  inner  root-sheath.  The 
substance  of  the  hair  is  composed  of  the  hair  fibres, 
i.e.,  long  thin  fibres,  or  narrow  long  scales,  each  com- 
posed of  hyaline  horny  substance,  and  possessed  of 
a  thin  staff-shaped  remnant  of  a  nucleus.  These 
are  held  together  by  a  certain  amount  of  interstitial 
cement  substance.  Towards  the  bulb  they  gradually 
change    into    the    spindle-shaped    cells   above    men- 


Chap.  XXXIV.] 


The  Skin. 


28 


a  I 


tioned.  They  can  be  isolated  by  strong  acids  and 
alkalies.  In  pigmented  hairs  there  occur  numerous 
pigment  granules  between  the  hair  fibres,  but  also 
diffused  pigment  in  their  substance.  The  same  is 
noticed  with  reference  to  the  hair-bulb — viz.,  pigment 
granules  being  present  in  the  intercellular  cement, 
and  pigment  also  in  the  cell  substance.  In  the  centre 
of  many  hairs  is  a  cylindrical  space,  containing  gene- 
rally one  row  of  polyhedral  cells,  which  are,  to  a  great 
extent,  filled  with  air,  and,  in  pigmented  hair,  also 
with  pigment  granules. 

384.  On  the  surface  of  the  hair  substance  is  a  thin 
cuticle,  a  single  layer  of  horny  non-nucleated  hyaline 
scales  arranged  more  or  less  transversely ;  they  are 
imbricated,  and,  according  to  the  degree  of  imbrica- 
tion, the  cuticle  shows  more  or  less 
marked  projections,  which  give  to  the 
circumference  of  the  hair  the  appear- 
ance of  minute  teeth,  like  those  of  a  saw. 

385.  The  inner  root-sheath  in  well- 
formed,  thick  hairs,  is  very  distinct, 
and  consists  of  a  delicate  cuticle  next 
to  the  cuticle  of  the  hair ;  then  an 
inner,  or  Huxley's,  layer,  which  is  a 
single,  or  sometimes  double,  layer  of 
horny  cubical  cells,  each  with  a  rem- 
nant of  a  nucleus ;  and,  finally,  an 
outer,  or  Henle's,  layer — a  single  layer 
of  non-nucleated  horny  cubical  cells. 

The   shaft    of   the   hair    (Fig. 
149),     or    the    part    projecting    over 
the  free  surface    of    the    skin,    is    of 
exactly  the  same  structure  as  the  root,  except  that  it 
possesses  no  inner  root-sheath. 

386.  As  mentioned  above,  at  the  hair-bulb  the 
polyhedral  cells  constituting  this  latter  gradually  pass 
into  the  different  parts  of  the  hair — i.e.,  marrow-sub- 


Fig.  149.  — Longitu- 
dinal View  of  the 
Shaft  of  a  Pig- 
mented Human 
Hair. 

a,  Marrow  of  hair ; 
b,  fibres  of  hair  sub- 
stance ;  c,  cuticle. 


284 


Elements  of  Histology.    [Chap,  xxxiv. 


stance,  cuticle,  and  inner  root-sheath — and  the  con- 
tinual new  production  of  cells  over  the  papilla  causes  a 

gradual  progression  and  con- 
version of  the  cells,  and  a 
corresponding  growth  in 
length  of  the  hair  shaft. 

Pigmented  hairs,  as  men- 
tioned above,  contain  pig- 
ment granules  between — i.e. , 
in  the  interstitial  substance 
cementing  together  —  the 
hair  fibres,  and  diffuse  pig- 
ment in  their  substance. 
According  to  the  amount 
of  these  pigments,  but  es- 
pecially of  the  interstitial 
pigment  granules  (Pincus), 
the  colour  of  the  hair  is  of 
a  greater  or  lesser  dark 
tint.  In  red  hairs  there  is 
chiefly  diffuse  pigment.  In 
white  or  fair  hairs  neither 
the  one  nor  the  other 
pigment  is  present ;  in  grey 
there  is  air  at  least  in 
the  superficial  layers  of  the 
hair  substance,  besides  ab- 
sence of  pigment. 

Sleek  hairs  are  circu- 
lar, curly  oval,  in  cross-sec- 
tion. 

387.  New  formation 
of  hair  (Fig.  150).  — 
Every  hair,  be  it  fine  and 
short  or  thick  and  long, 
under  normal  conditions, 
has    only   a    limited    exis- 


Fig.  150. — From  a  Section 

through  Human  Scalp,  showing 

a  degenerating  Hair. 

a.  The  epidermis ;  6,  the  hair  :  c,  the 
outer  root-sheath  of  the  hair  folli- 
cle ;  d,  the  sebaceous  follicle :  e,  the 
arrector  pili ;  /,  a  cyst  grown  out 
of  the  outer  root-sheath  ;  g,  the 
hair-knob ;  ft,  the  new  outgrowth 
of  the  outer  root-sheath;  i,  t)w 
new  papilla.  (Atlas.) 


chap,  xxxiv.]  The  Skin.  285 

tence,  for  its  hair-follicle,  including  the  papilla,  sooner 
or  later  undergoes  degeneration,  and  subsequent  to 
this  a  new  papilla  and  a  new  hair  are  formed  in  its 
place.  What  happens  is  this — the  lower  part  of 
the  hair-follicle,  including  the  papilla  and  hair-bulb, 
degenerates  and  is  gradually  absorbed.  Then  there 
is  left  only  the  upper  part  of  the  follicle,  and  in 
the  centre  of  this  is  the  remainder — i.e.,  non-degene- 
rated portion — of  the  hair  root.  The  fibres  of  this  are 
at  the  extremity  fringed  out  and  lost  amongst  the 
cells  of  the  outer  root-sheath  of  the  follicle.  This 
represents  the  hair-knob  (Henle).  Now,  from  the 
outer  root-sheath  a  cylindrical  outgrowth  of  epithe- 
lial cells  into  the  depth  takes  place ;  against  the 
extremity  of  this  a  new  papilla  is  made.  In  con- 
nection with  this  new  papilla,  and  in  the  centre  of 
that  cylindrical  outgrowth,  a  new  hair  and  hair-bulb 
are  formed,  and  as  these  gradually  grow  outwards 
towards  the  surface  they  lift,  or  rather  push,  the  old 
hair — i.e.,  the  hair-knob — out  of  the  follicle.  The 
outer  part  of  the  follicle  of  the  old  hair  persists. 

Thus  we  find  in  all  parts  of  the  skin  where  hairs 
occur,  complete  or  papillary  hairs  side  by  side  with 
degenerating  hairs,  or  hair-knobs. 

388.  Development  of  hair.— In  the  human 
fcetus  the  hair-follicles  make  their  first  appearance  about 
the  end  of  the  third  month,  as  solid  cylindrical  out- 
growths from  the  stratum  Malpighii.  This  is  the  rudi- 
ment of  the  outer  root-sheath.  After  having  pene- 
trated a  short  distance  into  the  corium,  this  latter  be- 
comes condensed  around  it  as  the  rudiment  of  the  hair- 
sac,  and  at  the  distal  extremity  forms  the  papilla 
growing  against  the  outer  root-sheath  and  inva- 
ginating  it.  In  connection  with  the  papilla  a  rapid 
multiplication  of  the  epithelial  cells  of  this  extremity 
of  the  outer  root-sheath  takes  place,  and  this  forms  the 
hair-bulb,  by  the  multiplication  of  whose  cells  the  hair 


286  Elements  of  Histology,    [chap,  xxxiv. 

and  the  inner  root-sheath  are  formed.  As  growth 
and  multiplication  proceed  at  the  hair-bulb,  so  the 
new  hair,  with  its  distal-pointed  end,  gradually  reaches 
the  outer  surface.  It  does  not  at  once  penetrate  the 
epidermis,  but  remains  growing  and  burrowing  its 
way  for  some  time  in  the  stratum  corneum  of  the 
epidermis  in  a  more  or  less  horizontal  direction. 

389.  In  many  mammals  occur,  amongst  ordinary 
hairs,  special  large  hairs,  with  huge  hair-follicles 
planted  deeply  into  the  subcutaneous  tissue ;  such 
are  the  big  hairs  in  the  skin  about  the  lips  of  the  mouth 
in  the  dog,  cat,  rabbit,  guinea-pig,  mouse  and  rat,  &c. 
These  are  the  tactile  hairs.  Their  hair-follicle  pos- 
sesses a  thick  hair-sac,  in  which  are  contained  large 
sinuses  intercommunicating  with  one  another  and 
with  the  blood  system ;  these  sinuses  are  separated  by 
trabecule  of  non-striped  muscular  tissue,  and  repre- 
sent, therefore,  a  cavernous  tissue.  The  papilla  is 
very  huge,  and  so  is  the  outer  root-sheath  and  the 
hair-root  in  all  its  parts.  There  are  vast  numbers  of 
nerve-fibres,  distributed  and  terminating  amongst  the 
cells  of  the  outer  root-sheath  (Arnstein). 

390.  With  each  hair-follicle  is  connected  one  or 
two  sebaceous  follicles.  These  consist  of  several  flask- 
shaped  or  oblong  alveoli,  joining  into  a  common  short 
duct  opening  into  the  hair-follicle  near  the  surface — 
i.e.,  that  part  called  the  neck  of  the  hair-follicle. 

The  alveoli  have  a  limiting  membrana  propria; 
next  to  this  is  a  layer  of  small  polyhedral,  granular- 
looking,  epithelial  cells,  each  with  a  spherical  or  oval 
nucleus ;  next  to  this,  and  filling  the  entire  space  of 
the  alveolus,  are  large  polyhedral  cells,  each  with  a 
spherical  nucleus;  the  cell- substance  is  filled  with 
minute  oil-globules,  between  which  is  left  a  sort  of 
honeycombed  reticulated  stroma.  The  cells  nearer  to 
the  centre  of  the  alveolus  are  the  largest.  To- 
wards the  duct  they  become  shrivelled   up   into    an 


chap,  xxxiv.]  The  Skin.  287 

amorphous  mass.  The  duct  itself  is  a  continuation  of 
the  outer  root-sheath. 

As  multiplication  goes  on  in  the  marginal  layer  of 
epithelial  cells — i.e..  those  next  the  membrana  propria 
— the  products  of  this  multiplication  are  gradually 
shifted  forward  towards  the  duct,  and  through  this 
into  the  neck  and  mouth  of  the  hair-follicle,  where 
they  constitute  the  elements  of  sebum. 

There  is  a  very  characteristic  misproportion  be- 
tween the  size  of  the  hair-follicle  and  that  of  the 
sebaceous  gland  in  the  embryo  and  new-born,  the 
sebaceous  gland  being  there  so  large  that  it  forms  the 
most  conspicuous  part,  the  minute  hairs  (lanugo)  being 
situated,  as  it  were,  in  the  duct  of  the  sebaceous 
follicle. 

391.  In  connection  with  each  hair-follicle,  espe- 
cially where  they  are  of  good  size — as  in  the  scalp — 
there  is  a  bundle,  or  rather  group  of  bundles,  of  non- 
striped  muscular  tissue  ;  this  is  the  arrector  pili.  It  is 
inserted  in  the  hair-sac  near  the  bulbous  portion  of  the 
hair-follicle,  and  passes  in  an  oblique  direction  towards 
the  surface  of  the  corium,  grasping,  as  it  were,  on  its 
way  the  sebaceous  follicle,  and  terminating  near  the 
papillary  layer  of  the  surface  of  the  corium.  The 
arrector  pili  forms  with  the  hair-follicle  an  acute 
angle — this  latter  being  planted  into  the  skin  in  an 
oblique  direction,  as  mentioned  above — and  conse- 
quently, when  the  arrector  contracts,  it  has  the  effect 
of  raising  the  hair  follicle  and  hair  (cutis  anserina — 
"goose's  skin"),  and  of  making  the  hair  assume  a 
more  upright  position  (causes  it,  as  we  say,  to  "stand 
on  end ").  At  the  same  time,  .it  compresses  the 
sebaceous  follicle,  and  thus  facilitates  the  discharge  of 
the  sebum. 

392.  The  corium  of  the  scrotum,  of  the  nipple  of 
the  breast,  of  the  labia  pudendi  majora,  and  of  the 
penis,   contains    numbers    of   bundles    of   non-striped 


288 


Elements  of  Histology,    [chap,  xxxiv. 


muscular  tissue  (Kolliker),  independent  of  the  hairs  ; 
these  run  in  an  oblique  and  horizontal  direction,  and 
form  plexuses. 

393.  The  Mails  (Fig.  151).— We  distinguish  the 
body  of  the  nail  from  the  free  margin  and  from  the 


Fig.  151.— Vertical  Section  th.rou.gn  the  Human  Nail  and  Nail-bed. 


a,  Stratum  Malpighii  of  nail-bed ;   6,  stratum  granulosum  of  nail-bed ;  c,  the 
deep  layers  of  the  nail  substance  ;  d,  the  superficial  layers  of  same. 


root ;  the  body  is  the  nail  proper,  and  is  fixed  on  to 
the  nail-bed,  while  the  nail-root  is  fixed  on  the  nail- 
matrix — i.e.,  the  posterior  part  of  the  nail-bed.  The 
nail  is  inserted,  with  the  greater  part  of  its  lateral 
and  the  posterior  margin,  in  the   nail-groove,  a  fold 


Chap,  xxxiv.]  The  Skin.  289 

by  which  the  nail-matrix  passes  into  the  surrounding 
skin. 

394.  The  substance  of  the  nail  is  made  up  of  a 
large  number  of  strata  of  homogeneous  horny  scales — 
the  nail-cells — each  with  a  staff-shaped  remnant  of  a 
nucleus. 

The  coriutn  of  the  nail-bed  is  highly  vascular ;  it 
is  firmly  fixed  by  stiff  bands  of  fibrous  tissue  on  the 
subjacent  periosteum ;  it  is  covered  with  a  stratum 
Malpighii  of  the  usual  description,  except  that  the 
stratum  granulosum  is  absent  in  the  nail-matrix,  but 
is  present  in  a  rudimentary  state  in  the  rest  of  the 
nail-bed.  The  nail  itself  represents  the  stratum 
lucidum,  of  course  of  exaggerated  thickness,  situated 
over  the  stratum  Malpighii  of  the  nail-bed.  There 
is  no  stratum  corneum  over  the  nail. 

The  stratum  Malpighii  and  corium  of  the  nail-bed 
are  placed  into  permanent  minute  folds,  and  the  nail 
possesses  on  its  lower  surface  corresponding  linear 
indentations. 

395.  In  the  foetal  nail-bed  the  stratum  Malpighii 
is  covered  with  the  usual  stratum  lucidum  and  stratum, 
corneum,  but  the  former  is  the  larger ;  by  a  rapid 
multiplication  of  the  cells  of  the  stratum  Malpighii, 
and  a  conversion  of  its  superficial  cells  into  the  scales 
of  the  stratum  lucidum,  the  foetal  nail  is  produced. 
At  this  early  stage  the  nail  is  covered  by  stratum 
corneum.  By  the  end  of  the  fifth  month  the  margin 
breaks  through  this  stratum  corneum,  and  by  the 
seventh  month  the  greater  part  has  become  clear 
of  it. 

396.  The  blood-vessels  of  the  skin.— The 
blood-vessels  are  arranged  in  different  systems  for  the 
different  parts  of  the  skin  (Tomsa) : — 

(a)  There  is,  first,  the  vascular  system  of  the 
adipose  tissue,  differing  in  no  way  from  the  dis- 
tribution of  blood-vessels  in  fat  tissue  of  other  places. 

T 


290  Elements  of  Histology.     [Chap,  xxxiv. 

(6)  Then  there  is  the  vascular  system  of  the  hair- 
follicles.  The  papilla  has  a  capillary  loop,  or  rather 
a  minute  arteriole,  a  capillary  loop,  and  a  descending 
vein,  and  the  fibrous  tissue  of  the  hair-sac  possesses 
capillaries  arranged  as  a  network  with  elongated 
meshes,  with  its  afferent  arteriole  and  efferent  vein. 

(c)  The  sebaceous  follicle  has  its  afferent  arteriole 
and  efferent  vein,  and  capillary  networks  surrounding 
the  alveoli  of  the  gland.  The  arrector  pili  and  other 
bundles  of  non-striped  muscular  tissue  possess  capil- 
lary networks  with  elongated  meshes. . 

(d)  The  sweat-glands  have  an  afferent  arteriole, 
from  which  proceeds  a  very  rich  network  of  capil- 
laries, twining  and  twisting  round  the  gland-tube. 
The  duct  possesses  its  separate  afferent  arteriole  and 
capillaries,  forming  elongated  meshes. 

(e)  The  last  arterial  branches  are  those  that  reach 
the  surface  of  the  corium,  and  there  break  up  into  a 
dense  capillary  network  with  loops  for  the  papillae. 
In  connection  with  these  capillaries  is  a  rich  plexus  of 
veins  in  the  superficial  layer  of  the  corium. 

(f)  In  the  nail-bed  are  dense  networks  of  capil- 
laries, with  loops  for  the  above-named  folds. 

397.  The  lymphatics. — There  are  networks  of 
lymphatic  vessels  in  all  strata  of  the  skin ;  they  are, 
more  or  less,  of  horizontal  expansion,  with  oblique 
branches  passing  between  them.  Their  wall  is  a 
single  layer  of  endothelial  cells,  and  some  of  them 
possess  valves.  Those  of  the  surface  of  the  corium 
take  up  lymphatics  of  the  papillae.  The  subcutaneous 
lymphatics  are  the  biggest.  The  fat  tissue,  the  sweat- 
glands,  and  the  hair-follicles  possess  their  own  lym- 
phatic clefts  and  sinuses.  The  interfascicular  spaces 
of  the  corium  and  subcutaneous  tissue  are  directly 
continuous  with  the  lymphatic  vessels  in  these 
parts. 

398.  The  nerves.— The  nerve-branches  break  up 


Chap,  xxxv.]    Conjunctiva  and  its  Glands.        291 

into  a  dense  plexus  of  fine  nerve-fibres  in  the  super- 
ficial layer  of  the  corium.  This  plexus  extends  hori- 
zontally, and  gives  off  numerous  elementary  fibrils 
to  the  stratum  Malpighii,  in  which  they  ascend  verti- 
cally and  in  a  more  or  less  wavy  fashion  towards  the 
stratum  lucidum  (Langerhans,  Podkopaeff,  Eberth, 
Eimer,  Ranvier,  and  others).  According  to  some,  they 
terminate  with  a  minute  swelling ;  according  to  others, 
they  form  networks ;  but  they  always  remain  between 
the  epithelial  cells. 

The  subcutaneous  nerve-branches  of  some  places 
— palm  of  hand  and  foot  and  skin  of  penis — give 
off  single  medullated  nerve-fibres,  terminating  in  a 
Pacinian  corpuscle,  mentioned  in  a  former  chapter. 
In  the  volar  side  of  the  fingers  and  toes  there  occur 
in  some  of  the  papillae  of  the  corium  the  tactile  or 
Meissner's  corpuscles,  each  connected  with  one  or  two 
medullated  nerve-fibres,  as  described  in  a  previous 
chapter.  The  outer  root-sheath  of  the  hair-follicles 
contains  the  terminations  of  fine  nerve-fibres,  in  the 
shape  of  primitive  fibrillse  (Jobert,  Bonnet,  and 
Arnstein).  According  to  Jobert,  the  nerve-fibres 
entwine  the  hair-follicle  in  circular  turns.  The  tactile 
hairs  possess  a  greater  supply  of  nerves  than  the 
ordinary  hair-follicles. 


CHAPTER,  XXXV. 

THE    CONJUNCTIVA   AND    ITS    GLANDS. 

399.  (1)  The  eyelids. — The  outer  layer  of  the 
eyelids  is  skin  of  ordinary  description ;  the  inner  is  a 
delicate,  highly  vascular  membrane — the  conjunctiva 
palpebrce.    This  includes  a  firm,  plate — the  tarsal-plate 


292  Elements  of  Histology.      [Chap,  xxxv 

— which  is  not  cartilage,  but  very  dense,  white,  fibrous 
tissue.  In  it  lie  embedded  the  Meibomian  glands. 
These  extend  in  each  eyelid  in  a  vertical  direction 
from  the  distal  margin  of  the  tarsal-plate  to  the  free 
margin  of  the  eyelid ;  in  the  posterior  angle  of  this 
margin  lies  the  opening  or  mouth  of  each  of  the 
Meibomian  glands. 

The  duct  of  a  Meibomian  gland  is  lined  with  a 
continuation  of  the  stratified  pavement  epithelium, 
lining  the  free  margin  of  the  lid ;  it  passes  in  the 
tarsal-plate  toward  its  distal  margin,  and  takes  up  on 
all  sides  short  minute  ducts,  each  of  which  becomes 
enlarged  into  a  spherical,  saccular,  or  flask-shaped 
alveolus.  This  is  identical  in  structure  and  secretion 
with  the  alveoli  of  the  sebaceous  follicles  of  the 
skin. 

400.  The  conjunctival  layer  is  separated  from  the 
subcutaneous  tissue  of  the  skin-layer  of  the  eyelid  by 
the  bundles  of  the  sphincter  orbicularis — striped  mus- 
cular tissue.  Some  bundles  of  this  extend  near  the 
free  margin  of  the  lid,  and  represent  what  is  known 
as  the  musculus  ciliaris  Riolani.  This  sends  bundles 
around  the  mouth  of  the  Meibomian  ducts. 

401.  At  the  anterior  angle  of  the  free  margin  of 
the  lid  are  the  eyelashes  or  cilia,  remarkable  for  their 
thickness  and  rapid  reproduction.  Near  the  cilia,  but 
towards  the  Meibomian  ducts,  open  the  ducts  of  pecu- 
liar large  glands — the  glands  of  Mold.  Each  of  these 
is  a  wavy  or  spiral  tube,  passing  in  a  vertical  direction 
from  the  margin  of  the  lid  towards  its  distal  part ;  it 
completely  coincides  in  structure  to  the  large  portion 
of  a  sweat  gland — i.e.,  that  part  containing  a  columnar 
epithelial  lining,  and  between  this  and  the  membrana 
propria  a  longitudinal  layer  of  non-striped  muscular 
cells. 

The  free  margin  is  covered,  as  mentioned  above, 
with  stratified  pavement  epithelium,  into  which  the 


chap,  xxxv.]    Conjunctiva  and  its  Glands.       293 

mucous  membrane  extends  in  the  shape  of  minute 
papillae.  In  the  conjunctiva  palpebrae  the  epithelium 
is  thin,  but  stratified  pavement  epithelium;  there  are 
no  papillae,  but  the  sub-epithelial  mucosa — that  is,  the 
layer  situated  between  the  epithelium  of  the  surface 
and  the  tarsal-plate — ^contains  a  dense  network  of 
capillary  blood-vessels. 

402.  Passing  from  the  eyelids  on  to  the  eyeball, 
we  have  the  continuation  of  the  conjunctiva  palpebrae 
— i.e.,  the  fornix  conjunctivae — and,  further,  the  con- 
junctiva fixed  to  the  sclerotic,  and  terminating  at  the 
margin  of  the  cornea — the  conjunctiva  bulbi.  The 
epithelium  covering  the  conjunctiva  fornicis  and  con- 
junctiva bulbi  is  stratified  epithelium,  the  superficial 
cells  being  short  columnar;  next  to  the  fornix  the 
superficial  cells  are  beautiful  columnar,  and  the 
mucosa  underneath  the  epithelium  is  placed  in  regular 
folds  (Stieda,  Waldeyer).  Towards  the  cornea  the 
epithelium  of  the  conjunctiva  assumes  the  character 
of  stratified  pavement  epithelium,  and  minute  papillae 
extend  into  it  from  the  mucosa. 

403.  The  mucous  membrane  is  fibrous  tissue, 
containing  the  networks  of  capillary  blood-vessels. 

Into  the  fornix  lead  minute  mucous  glands,  em- 
bedded in  the  conjunctiva  fornicis  ;  they  are  the  glands 
of  Krause.  Similar  glands  exist  in  the  distal  portion 
of  the  tarsal-plate. 

404.  The  Mood-vessels  of  the  conjunctiva  ter- 
minate as  the  capillary  network  of  the  superficial 
layer  of  the  mucosa,  and  as  capillary  networks  for  the 
Meibomian  glands,  Krause's  gland,  &c.  Around  the 
corneal  margin  the  conjunctival  vessels  are  particu- 
larly dense,  and  loops  of  capillaries  extend  from  it 
into  the  very  margin  of  the  cornea. 

405.  The  lymphatics  form  a  superficial  and 
deep  network.  Both  are  connected  by  short  branches. 
The  deep  vessels  are  possessed  of  valves.     The  super- 


294  Elements  of  Histology,      [Chap.  xxxv. 

ficial  plexus  is  densest  at  the  limbus  cornese,  and  they 
are  in  direct  connection  with  the  interfascicular 
lymph  clefts,  both  of  the  sclerotic  and  cornea.  In 
the  margin  of  the  lid  the  superficial  lymphatics  of 
the  skin  anastomose  with  those  of  the  conjunc- 
tiva. 

Lymph  follicles  occur  in  groups  in  the  conjunctiva 
of  many  mammals  about  the  inner  angle  of  the  eye. 
In  the  lower  eyelid  of  cattle  they  are  very  con- 
spicuous, and  known  as  the  glands  of  Bruch.  They 
are  also  well-marked  in  the  third  lid  of  many 
mammals. 

According  to  Stieda  and  Morano,  isolated  lymph 
follicles  occur  also  in  the  human  conjunctiva. 

406.  The  nerves  are  very  numerous  in  the  con- 
junctiva ;  they  form  plexuses  of  non-medullated  fibres 
underneath  the  epithelium.  From  these  plexuses  fine 
fibrils  pass  into  the  epithelium  of  the  surface,  between 
whose  cells  they  terminate  as  a  network  (Helfreich, 
Morano).  End  bulbs  of  Krause  occur  in  great  num- 
bers in  man  and  calf.  They  have  been  mentioned  in 
a  former  chapter. 

407.  (2)  The  lachrymal  glands  are  identical 
in  structure  with  the  serous  or  true  salivary 
glands.  The  arrangement  of  the  connective  tissue 
stroma,  the  nature  and  structure  of  the  ducts — espe- 
cially of  the  intralobular  ducts — and  alveoli,  the  dis- 
tribution of  blood-vessels  and  lymphatics,  are  exactly 
the  same  as  in  the  true  salivary  glands.  Reichel 
has  found  that  the  epithelial  cells  lining  the 
alveoli  are  well  defined,  conical  or  cylindrical,  trans- 
parent and  slightly  granular  during  rest ;  but 
during  secretion  they  grow  smaller,  more  opaque 
and  granular,  their  outlines  not  well  defined,  and 
the  nucleus  becomes  more  spherical  and  placed  more 
centrally. 

408.  In   most   mammals   there    is   in    the   inner 


chap,  xxxvi.]  The  Cornea.  295 

angle  of  the  eye,  and  closely  placed  against  the  sur- 
face of  the  eyeball,  a  gland,  called  Hardens  gland. 
According  to  Wenclt,  this  is  either  a  true  serous 
gland,  like  the  lachrymal — as  in  the  ox,  sheep,  and 
pig — or  it  is  identical  in  structure  with  a  sebaceous 
gland,  as  in  the  mouse,  rat,  and  guinea-pig  ;  or  it 
consists  of  two  portions,  one  of  which  (white)  is 
identical  with  a  sebaceous,  while  the  other  (rose- 
coloured)  is  a  true  serous  gland;  such  is  the  case  in 
the  rabbit  and  hare.  According  to  Giacomini,  a 
rudiment  of  Harder's  gland  exists  also  in  the  ape 
and  man. 


CHAPTER  XXXYI. 

THE   COENEA,    SCLEROTIC,    LIGAMENTUM    PECTINATUM, 
AND    CILIARY   MUSCLE. 

409.  I.  The  cornea  (Fig.  152)  of  man  and  many 
mammals  consists  of  the  following  layers,  counting 
from  front  to  back  : — 

(1)  The  epitlielium  of  the  anterior  surface  (see 
Fig.  15) ;  this  is  a  very  transparent,  stratified,  pave- 
ment epithelium,  such  as  has  been  described  in  par. 
22.  It  is  directly  continuous  with  the  epithelium  of 
the  conjunctiva,  but  it  is  more  transparent ;  in  dark 
pigmented  eyes  of  mammals  the  epithelium  of  the 
conjunctiva  is  also  pigmented.  In  these  cases  the 
pigment,  as  a  rule,  does  not  pass  beyond  the  margin 
of  the  cornea. 

410.  (2)  Next  follows  a  homogeneous  elastic  mem- 
brane, Bowman's  membrane,  or  elastica  anterior.  It 
is  best  shown  in  the  human  eye,  but  is  present,  even 
though  only  rudimentary,  in  the  eye  of  mammals. 


296 


Elements  of  Histology-    [Chap,  xxxvi. 


(3)  Then  follows  the  ground  substance,  or  sub- 
stantia propria,  of  the  cornea.     This  is  composed  of 

lamellae  of  bundles 
of  fibrous  connective 
tissue.  Neighbouring 
lamellae  are  connected 
with  one  another  by 
oblique  bundles. 

The  fibre  bundles 
within  each  lamella 
run  parallel  to  the  sur- 
face of  the  cornea,  but 
may  cross  one  another 
under  various  angles. 

In  the  anterior 
layer  of  the  ground 
substance  some  of  the 
bundles  pass  through 
several  lamellae  in  an 
oblique  manner ;  they 
represent  the  fibrae 
arcuatae. 

The  fibrils  within 
the  bundles,  and  the 
bundles,  and  the  la- 
mellae of  bundles  are 
held  together  by  an 
interstitial,  albumin- 
ous, semi-fluid,  cement 
substance,  which,  like 
other  similar  intersti- 
tial substances,  be- 
longs to  the  globulins, 
and  is  soluble  in  10 
per  cent,  saline  solu- 
tion (Schweigger  Sei- 
del).      A  few  elastic 


Fig.  152. — From  a  Vertical  Section 
through  the  Membranes  of  the  Eye 
of  a  Child. 

a,  Cornea;  b,  sclerotic:  c,  iris;  d,  processus 
ciliaris;  e,  ligamentum  pectinatum ;  /, 
ciliary  muscle,  its  meridional  bundles : a, 
choroid  membrane  ;  h,  the  retina  of  the  ora 
Berrata;  •*,  the  sphincter  pupillaa  in  cross 
section.    (Atlas.) 


chap,  xxxvi.]  The  Cornea.  297 

fibrils  are  seen  here  and  there.  Between  the  lamellae 
are  left  the  lacunae  and  canaliculi  for  the  branched, 
flattened,  nucleated  corneal  corpuscles,  described  in 
a  previous  chapter  (Figs.  25,  26).  They  anasto- 
mose with  one  another  within  the  same  plane,  and 
also,  to  a  limited  degree,  with  those  of  neighbouring 
planes. 

411.  (4)  The  membrana  Descemeti,  or  elastica 
posterior,  is  a  resistent  elastic  membrane,  conspicuous 
by  its  thickness  in  all  corneae. 

(5)  The  posterior  surface  of  this  membrane  is 
covered  with  a  mosaic  of  beautiful  polygonal  endo- 
thelial cells,  each  with  an  oval  nucleus — the  en- 
dothelium of  Descemet's  membrane.  Under  stimu- 
lation these  cells  contract.  At  first  they  appear 
slightly  and  numerously  branched,  but  gradually 
their  processes  become  longer  and  fewer,  and 
ultimately  they  are  reduced  to  minute  clumps 
of  nucleated  protoplasm,  each  with  a  few  long  pro- 
cesses. 

There  are  no  blood-vessels  in  the  normal  cornea, 
except  in  festal  life,  when  there  is  underneath  the 
anterior  epithelium  a  plexus  of  capillaries. 

The  lymphatics  are  represented  as  the  inter- 
communicating lymph-canalicular  system — i.e.,  the 
lacunas  and  canaliculi  of  the  corneal  corpuscles ;  and 
in  connection  with  these  are  lymph  channels  lined 
with  a  continuous  endothelium  and  containing  the 
nerve  bundles. 

412.  The  nerves  (Figs.  68,  69,  70)  are  distri- 
buted as  the  nerves  of  the  anterior  layers,  and  as 
those  of  the  Descemet's  membrane.  The  first  form 
rich  plexuses  of  fibrillated  axis  cylinders,  with  trian- 
gular nodal  points  (Cohnheim),  in  the  anterior  layers  of 
the  ground  substance  \  from  this  plexus  pass  obliquely 
through  Bowman's  membrane  short  branches — the 
rami   perforantes   (Kolliker) — and  these  immediately 


298  Elements  of  Histology.     [Chap,  xxxvi. 

underneath  the  epithelium  break  up  into  their  con- 
stituent primitive  fibrils,  the  latter  coming  off  the 
former  brush-like  (Cohnheim).  These  primitive 
fibrillar  ultimately  ascend  into  the  anterior  epithelium 
(Hoyer,  Cohnheim,  and  others),  where  they  branch, 
and  nearly  reach  the  surface.  They  always  run 
between  the  epithelial  cells,  and  are  connected  into 
a  network.  According  to  some  observers,  they  termi- 
nate with  free  ends,  pointed  or  knobbed ;  but  according 
to  others,  with  whom  I  agree,  these  apparent  free  ends 
are  not  in  reality  free  endings. 

413.  The  nerves  of  Descemet's  membrane  form 
also  a  plexus  of  non-medullated  fibres  in  the  posterior 
layers  of  the  ground  substance;  from  them  come 
off  vast  numbers  of  primitive  fibrillar,  running  a  more 
or  less  straight  and  long  course,  crossing  one  another 
often  under  right  angles ;  they  give  off  very  fine 
fibrils,  which  are  closely  associated  with  the  corneal 
corpuscles,  without,  however,  really  becoming  con- 
tinuous with  their  protoplasm. 

414.  II.  The  sclerotic  consists  of  lamellae  of 
tendinous  tissue.  The  bundles  of  fibrous  tissue  are 
opaque  as  compared  with  those  of  the  cornea,  although 
they  pass  insensibly  into  them.  There  are  lymph 
clefts  between  the  lamellae  and  trabecular,  and  in 
them  lie  the  flattened  connective  tissue  corpuscles, 
which,  in  the  dark  eyes  of  some  mammals  only,  contain 
pigment  granules.  Numerous  elastic  fibrils  are  met 
with  in  the  inner  layers  of  the  sclerotic. 

415.  Between  the  sclerotic  and  choroid  membrane 
is  a  loose  fibrous  tissue,  which  acts  also  as  the  sup- 
porting tissue  for  the  blcod- vessels  passing  to  and  from 
the  choroid.  The  part  of  this  loose  tissue  next 
to  the  sclerotic,  and  forming  part,  as  it  were,  of 
the  sclerotic,  contains,  in  dark  eyes  of  mammals, 
numerous  pigmented  connective  tissue  corpuscles ;  it 
is   then   called   lamina  fusca.      The  rest — i.e.,   next 


Chap.  XXXVI.]       LlGAMENTUM  fECTINATUM.  2Qg 

to   the   choroid    membrane — is    the    supra-choroidai 
tissue. 

416.  There  are  blood-vessels  in  the  sclerotic,  which 
belong  to  it :  they  are  arterioles,  capillaries,  and 
veins  ;  in  addition  to  these  are  the  vascular  branches 
passing  to  and  from  the  choroid. 

417.  III.  The  ligamentum  pectinatum 
iridis  (see  Fig.  152)  is  a  conical  mass  of  spongy  tissue, 
joining  firmly  the  cornea  and  sclerotic  to  the  iris  and 
ciliary  processes.  It  forms  an  intimate  connection,  on 
the  one  hand,  with  the  junction  of  cornea  and  sclerotic, 
and  on  the  other,  with  that  of  the  iris  and  ciliary  pro- 
cesses. This  ligament  is  composed  of  trabecule  and 
lamellae  of  stiff  elastic  fibres,  forming  a  continuity,  on 
the  one  hand,  with  the  lamina  Descemeti  of  the  cornea 
and  the  elastic  fibres  of  the  sclerotic,  and  on  the  other, 
with  the  tissue  of  the  ciliary  border  of  the  iris.  The 
trabecular  anastomose,  so  as  to  form  a  honeycombed 
plexus,  and  the  spaces  in  this  plexus  are  lined 
with  a  layer  of  flattened  endothelial  cells,  directly 
continued  from  the  endothelium  of  Descemet's  mem- 
brane, on  the  one  hand,  and  with  the  layer  of  endo- 
thelial cells  covering  the  anterior  surface  of  the  iris, 
on  the  other  hand.  In  some  mammals,  the  spaces 
in  the  ligamentum  pectinatum  at  the  iris  end  are 
very  considerable,  and  are  called  the  spaces  of 
Fontana. 

The  interlamellar  and  interfascicular  lymph- 
spaces  of  the  sclerotic  form  an  intercommunicating 
system. 

The  nerves  form  a  dense  plexus  of  non-medullated 
fibres  in  the  tissue  of  the  sclerotic  (Helfreich). 

At  the  point  of  junction  of  the  cornea  and  sclerotic, 
but  belonging  to  the  latter,  and  in  the  immediate 
neighbourhood  of  the  ligamentum  pectinatum  iridis, 
is  a  circular  canal— the  canal  of  Schlemm;  this  is 
lined  with  endothelium,  and  is  considered  by  some 


300  Elements  of  Histology.   [Chap,  xxxvn. 

(Schwalbe)  as  a  lymphatic  canal;  by  others  (Leber) 
as  a  venous  vessel. 

418.  IV.  The  ciliary  muscle  (Fig.  152)  or 
tensor  choroidese,  is  fixed  to  this  ligamentum  pecti- 
natuin ;  it  is  composed  of  bundles  of  non-striped 
muscular  tissue.  This  muscle  consists  of  two  parts : 
(a)  one  of  circular  bundles  nearest  to  the  iris — this 
is  the  portio  Miilleri  ;  (b)  the  greater  part  is  composed 
of  radiating  bundles,  passing  from  the  ligamentum 
pectinatum  in  a  meridional  direction  for  a  consider- 
able distance  backwards  into  the  tissue  of  the  choroid 
membrane.  It  occupies  the  space  between  the  liga- 
mentum pectinatum,  sclerotic,  ciliary  processes,  and 
the  adjoining  portion  of  the  choroid  membrane. 
The  bundles  of  the  muscle  are  arranged  more 
or  less  in  lamellae;  within  each  lamella  they  form 
plexuses. 

A  rich  plexus  of  non-medullated  nerve-fibres,  with 
groups  of  ganglion  cells,  belongs  to  the  ciliary  muscle. 


CHAPTER  XXXVII. 

THE    IRIS,    CILIARY    PROCESSES,    AND    CHOROIDEA. 

419.  I.  The  iris  consists  of  the  following  layers : — 

(1)  The  endothelium  of  the  anterior  surface  :  trans- 
parent, flattened,  or  polyhedral  cells,  each  with  a 
spherical  or  slightly  oval  nucleus  ;  in  dark-coloured 
eyes  of  man  and  mammals  brown  pigment  granules 
are  contained  in  the  cell-substance. 

(2)  A  delicate  hyaline  basement  membrane  :  it  is 
continuous  through  the  trabecular  of  the  ligamentum 
pectinatum,  with  the  membrana  Descemeti  of  the 
cornea. 


chap,  xxxvii.]  The  Iris.  301 

(3)  The  substantia  propria :  this  is  the  ground- 
substance  ;  it  consists  of  fibrous  connective  tissue  in 
bundles,  accompanying  the  blood-vessels,  which  are 
very  numerous  in  the  tissue  of  the  iris.  Many 
connective  tissue  corpuscles  are  found  in  the  sub- 
stantia propria ;  they  are  more  or  less  branched,  and 
many  of  them  contain,  in  all  but  albino  and  blue 
eyes,  yellowish-brown  pigment  granules.  The  colour 
of  the  iris  varies  according  to  the  number  of  these 
pigmented  connective  tissue  cells,  and  to  the  amount 
of  the  pigment  granules  present  in  them. 

(4)  A  hyaline  delicate  basement  membrane  limits 
the  substantia  propria  at  the  posterior  surface  ;  this 
is  an  elastic  membrane,  and  is  continued  over  the 
ciliary  processes  and  choroid  as  the  lamina  vitrea. 

420.  (5)  The  last  layer  is  the  epithelium  of  the 
posterior  surface  :  this  is  a  layer  of  polyhedral  cells, 
filled  with  dark  pigment  granules,  except  in  albinos, 
where  there  are  no  pigment  granules.  This  endo- 
thelium is  called  the  uvea,  or  tapetum  nigrum.  The 
interstitial  cement  substance  between  the  cells  is  not 
pigmented,  but  transparent. 

The  name  "  uvea "  is  sometimes  applied  to  the 
whole  of  the  iris,  ciliary  processes,  and  choroid  mem- 
brane. 

In  blue  eyes  the  posterior  epithelium  is  the  only 
pigmented  part  of  the  iris,  and  so  it  is  also  in  the 
iris  of  new-born  children  ;  hence,  their  eyes  are  blue. 
Such  iris  appears  blue  because  its  dull  tissue  is  viewed 
on  dark  ground — i.e.,  on  the  pigmented  epithelium  of 
the  posterior  surface. 

421.  Near  the  pupillary  border  the  posterior  sec- 
tion of  the  substantia  propria  contains  a  broad  layer 
of  circular  bundles  of  non-striped  muscular  tissue  : 
this  is  the  sphincter  pupillce.  In  connection  with  this 
are  bundles  of  non-striped  muscular  fibres,  passing  in 
a  radiating  direction  towards  the  ciliary  margin  of  the 


302 


Elements  of  Histology.    [Chap,  xxxvu. 


■H.'iii'S'-Tllli.ml  1"  '  '   i    '.'"   '.  1'' 


iris :  these  are  the  bundles  of  the  dilatator  pupillaz, 
forming  a  sort  of  thin  membrane  near  the  posterior 
surface  of  the  iris  (Henle  and  others).     At  the  ciliary 

margin  the  bundles  take  a 
circular  direction,  and  form  a 
plexus  (Ivanoff). 

422.  The  blood-vessels 
(Fig.  153)  of  the  iris  are 
very  numerous.  The  arteries 
are  derived  from  the  circulus 
arteriosus  iridis  major,  situated 
at  the  ciliary  margin  of  the 
iris,  and  from  the  arteries  of 
the  ciliary  processes.  These 
arteries  run  in  a  radiating 
direction  towards  the  pupillary 
margin,  where  they  terminate 
in  a  dense  network  of  capillaries 
for  the  sphincter  pupillse.  But 
there  are  also  numerous  capil- 
lary blood-vessels  of  a  more  or 
less  longitudinal  direction  near 
the  posterior  surface  of  the  iris. 
The  veins  accompany  the  arte- 
ries, and  both  are  situated  in 
the  middle  stratum  of  the 
substantia  propria. 

In  the  sheath  of  the  blood- 
vessels are  lymph  clefts  and 
lymph  sinuses  ;  there  appear  to 
be  no  other  lymphatics. 

423.  The  nerve  -  fibres 
are  very  numerous  (Arnold, 
Formad),  and  in  the  outer  or 

ciliary  portion  of  the  iris  form  a  rich  plexus,  from 
which  are  derived,  (a)  networks  of  non-medullated 
fibres  for  the  dilator  pupillse ;   (b)  a  network  of  fine 


Fig.  153.  —  Blood-vessels 
(injected)  of  the  Iris 
and  Choroid  Membrane 
of  the  Eye  of  a  Child. 

«,  Capillaries  of  the  choroid ; 
b,  ora  serrata ;  c,  blood- 
vessels derived  from  d, 
those  of  the  ciliary  pro- 
cesses, and  from  e,  those 
of  the  iris  ;  /,  capillary  net- 
work of  the  pupillary  bor- 
der. (KOlliker,  after  Arnolds 


Chap,  xxxvii.]    The  Ciliary  Process.  303 

non-medullated  fibres  for  the  anterior  surface ;  and 
(c)  a  network  of  non-medullated  fibres  for  the 
sphincter  pupillse. 

The  capillary  blood-vessels  are  also  accompanied 
by  fine  nerve-fibres  (A.  Meyer),  and,  according  to 
Faber,  there  exist  ganglion  cells  in  these  nerve  net- 
works. 

424.  II.  The  ciliary  processes  are  similar  in 
structure  to  the  iris,  except,  of  course,  that  they  do 
not  possess  an  anterior  endothelium  or  an  anterior 
basement  membrane.  The  substantia  propria  is 
fibrous  tissue  with  elastic  fibres  and  numerous 
branched  cells,  pigmented  in  dark  (but  not  in  blue) 
eyes.  The  posterior  basement  membrane  is  very 
thick,  and  is  called  the  lamina  vitrea ;  in  it  may  be 
detected  bundles  of  fine  fibrils.  It  possesses  perma- 
nent folds  arranged  in  a  network  (H.  Muller).  The 
inside  of  it  is  covered  with  a  layer  of  pigmented  poly- 
hedral epithelium,  the  tapetum  nigrum:  the  cells  are 
polygonal  when  viewed  from  the  surface.  The  in- 
dividual cells  are  separated  by  thin  lines  of  a  trans- 
parent cement  substance.  This  pigmented  epithelium 
is  covered  with  a  layer  of  transparent  columnar 
epitheloid  cells,  each  with  an  oval  nucleus.  These  are 
closely  fixed  on  the  tapetum  nigrum,  and  represent  a 
continuation  of  the  retina  over  the  ciliary  processes  : 
this  is  the  pars  ciliaris  retinas  (Fig.  154). 

425.  The  arterial  branches  for  the  ciliary  processes 
and  muscle  are  chiefly  derived  from  the  circulus  arte- 
riosus iridis  major,  and  form  a  dense  network  of 
capillaries  for  the  former;  to  each  of  these  corre- 
sponds a  conical  group  of  capillaries  (Fig.  153). 

426.  III.  The  choroid  membrane  consists — 
counting  from  outwards,  i.e.,  from  the  sclerotic,  inwards, 
i.e.,  towards  the  retina — of  the  following  layers  : — 

(1)  The  membrana  supra-choroidea.  This  is  a 
continuation  of  the  sclerotic,  with  which  it  is  identical 


3°4 


Elements  of  Histology.    [Chap,  xxxvn. 


in 


are 


structure ;    the   spaces   between   its   lamellae 
lined  with  endothelium,  and  represent  lymph  spaces 
(Schwalbe). 

(2)  Next  follows  an  elastic  layer  which  contains 
networks  of  elastic  fibres,  the  branches  of  the  arteries 


Fig.  154— From  a  Vertical  Section  through  the  Ciliary  Processes  of 
the  Ox's  Eye. 

a,  Fibrous  tissue  with  pigmented  cells ;  6,  loose  fibrous  tissue  forming  the 
proper  membrane  of  the  ciliary  process  ;  c,  the  pigmented  epithelium  covering 
the  posterior  surface  of  the  ciliary  process ;  d,  the  epitheloid  cells,  forming 
the  pars  ci Maris  retinas  covering  the  back  of  the  ciliary  processes  ;  e,  Zonula 
Zinnii,  with  bundles  of  fibres.    lAtlas.) 

and  veins,  and,  in  its   outer  portion,  pigmented   cells 
(Fig.  155).  < 

427.  (3)  Then  follows  the  membrana  chorio- 
capillaris,  a  dense  network  of  capillary  blood-vessels 
embedded  in  a  tissue  containing  numerous  branched 


■%?J 


chap,  xxxviii.]  The  Lens.  305 

and  unbranched  pigmented  and  unpigmented  connec- 
tive-tissue cells. 

(4)  The  lamina  vitrea  ;  and,  finally, 

(5)  The  tapetum  nigrum,  or  the  pigmented  epithe- 
lium, which,  however,  is  considered  part  of  the 
retina.  In  the  region  of  the  ora  serrata  of  the 
retina  also — i.e.,  next 

to  the  ciliary  processes  ..*%•.;  „*=.-.-.. 

— this  zone  of  the 
choroidea  is  lined 
with  a  layer  of  trans- 
parent, columnar, 
ej)itheloid  cells,  re- 
presenting   the    pars 

•v      .         ?•  Fiff.  155.— Pigmented  Connective  Tissue 

cilians  retinae.  gells  o£  th|  choroid  Coat.    (Atlas.) 

428.  The  arfcerise 
ciliares  breves  and  recurrentes,  situated  in  the  outer 
part  of  the  choroidal  tissue,  form  ultimately  the  dense 
networks  of  capillaries  for  the  chorio-capillaries.  The 
veins  derived  from  this  pass  into  the  outer  part  of 
the  choroid,  where  they  anastomose  so  as  to  form  the 
peculiar  large  veins,  which  are  called  the  venae 
vorticosee. 


CHAPTER   XXXVIII. 

THE    LENS    AND    VITREOUS    BODY. 

429.  (1)  The  lens  consists  of  a  thick,  firm,  elastic 
capsule  and  of  the  lens  substance.  The  former  shows 
fine  longitudinal  stria?,  and  diminishes  in  thickness 
towards  the  posterior  pole  of  the  lens.  The  surface 
of  the  capsule  facing  the  anterior  surface  of  the  lens- 
substance  is  lined  with  a  single  layer  of  polyhedral, 
granular-looking,  epithelial  cells,  each  with  a  spherical 
or  oval  nucleus.  This  epithelium  stops  as  such  at  the 
U 


3°6 


Elements  of  Histology.   [Chap,  xxxviii. 


margin  of  the  lens,  where  its  cells,  gradually  elonga- 
ting, pass  into  the  lens-fibres.  The  nuclei  of  these 
lie  in  a  curved  plane  belonging  to  the  anterior  half  of 
the  lens  :  this  is  the  miclear  zone.  The  lens-substance 
consists  of  the  lens-fibres.  These  are  band-like,  hexa- 
gonal in  transverse  section ;  their  outline  is  beset 
with  numerous  fine  ridges  and  furrows,  which  in 
neighbouring  fibres,  fitting  the  one  into  the  other, 
form  a  firm  connection  between  the  fibres  (Valentin, 
Henle,  Kolliker,  and  others).  The  fibres  of  the 
peripheral  portion  are  broader  and  thicker,  and  their 
substance  less  firm  than  those  of  the  centre — i.e.,  of 
the  lens-nucleus.  The  substance  of  the  lens-fibres  is 
finely  granular  and  delicately  and  longitudinally 
striated. 

430.  The  lens  fibres  (Fig.  156)  are  arranged  in 
concentric  lamellae,  each  consisting  of  a  single  layer  of 

fibres  joined  by  their  broad 
surfaces.  Each  fibre  is  slightly 
enlarged  at  the  extremities ; 
and  in  each  lamella  the  fibres 
extend  from  the  anterior  to  the 
posterior  surface.  Their  ex- 
tremities are  in  contact  with 
the  ends  of  the  fibres  of  the 
same  lamella  in  the  sutures,  or 
the  rays  of  the  so-called  lens 
stars.  In  the  lens  of  the  new- 
born child,  the  stars  of  both 
anterior  and  posterior  lamellae 
possess  three  such  rays,  while 
in  the  adult  each  of  these  rays 
has  secondary  rays.  In  these 
rays  there  is  a  homogeneous  thin  layer  of  an  albu- 
minous cement  substance ;  a  similar  substance  in 
minute  quantity  is  also  present  between  the  lamella3, 
and  in  it  occur  smaller  or  larger  clefts  and  channels, 


tf^fffffff^f'ff 


W/U^AAM^'^'^  <^ 


Fig.  156. — From  a  Section 
through  the  Lens  of 
Dog. 

Showing  four  lamellae ;  in 
each  the  component  lens- 
flbres  are  cut  across;  they 
appear  as  flattened  hexa- 
gons.   (Atlas.) 


chap,  xxxviii.]    The   Vitreous  Body.  307 

which  evidently  carry  the  nutritious  fluid  for  the  lens- 
fibres. 

431.  (2)  The  vitreous  body  is  a  fluid  substance 
enclosed  in  a  delicate  hyaline  capsule — the  membrana 
hyaloidea.  This  membrane,  at  the  margin  of  the 
fossa  patellaris  of  the  vitreous  body — i.e.,  the  fossa  in 
which  the  lens  is  lodged — but  without  covering  it, 
passes  as  the  zonula  ciliaris,  or  zonula  Zinnii,  or 
suspensory  ligament  of  the  lens,  to  the  margin  of  the 
latter,  to  which  it  is  firmly  adhering.  So  it  adheres 
also  to  the  surface  of  the  ciliary  processes.  The 
zonula  Zinnii  is  hyaline  and  firm,  and  is  strengthened 
by  numbers  of  bundles  of  minute  stiff  fibrils. 

Between  the  suspensory  ligament  of  the  lens,  the 
margin  of  the  lens  and  of  the  fossa  patellaris  is  a 
circular  lymph  space,  called  the  canalis  Petiti. 

Beneath  the  membrana  hyaloidea  are  found  iso- 
lated nucleated  granular-looking  cells  (the  subhyaloid 
cells  of  Ciaccio),  possessed  of  amoeboid  movement 
(Ivanoff). 

432.  The  substance  of  the  corpus  vitreum  appears 
differentiated  by  clefts,  concentric  in  the  peripheral, 
radiating  in  the  central,  part  (Brticke,  Hannover, 
Bowman,  Ivanoff,  Schwalbe).  But  these  do  not 
contain  any  distinct  membranous  structures  (Stilling, 
Ivanoff,  Schwalbe). 

The  canalis  hyaloideus,  or  canal  of  Stilling,  extends 
from  the  papilla  nervi  optici  to  the  posterior  capsule 
of  the  lens,  and  is  lined  with  a  continuation  of  the 
membrana  hyaloidea. 

433.  In  the  substance  of  the  corpus  vitreum  occur 
isolated  nucleated  cells  ;  they  have  amoeboid  move- 
ments, and  some  contain  vacuoles,  from  commencing 
degeneration.  They  are  all  identical  with  white 
blood-corpuscles  (Lieberkuhn,  Schwalbe). 

Fine  bundles  of  fibrils  are  occasionally  seen  in  the 
substance  of  the  vitreous  body. 


3o8 


[Chap.  XXXIX. 


CHAPTER   XXXIX. 


THE    RETINA. 


G  ©  ©  ®  ©  Q)  @®  ©  ©  q  ©  ©  <J  ^  0  o1 


434.  The  retina  (Fig.  157)  consists  of  the  following 
layers,  counting  from  inwards  towards  the  choroid  mem- 
brane:—  (1)  The 
membrana  limitans 
interna,  which  is 
next  to  the  mem- 
brana hyaloidea  of 
the  vitreous  body ; 
(2)  the  nerve-fibre 
layer;  (3)  the  layer 
of  ganglion  cells; 
(4)  the  inner  gran- 
ular or  inner  mole- 
cular layer ;  (5)  the 
layer  of  inner 
nuclei ;  (6)  the 
outer  granular,  or 
outer  molecular,  or 
internuclear  layer ; 
(7)  the  layer  of 
outer  nuclei ;  (8) 
the  membrana 
limitans  externa  ; 
(9)  the  layer  of 
rods  and  cones ; 
and  (10)  the  pig- 
mented epithelium 
of  the  retina,  or  the  tapetum  nigrum  mentioned  above, 
which  forms,  at  the  same  time,  the  inner  lining  epithe- 
lium of  the  choroid  membrane. 


Eig.  157.— From  a  Transverse  Section 
through  the  Eye  of  Sheep ;  Peripheral 
Portion  of  Retina. 

a,  The  inner  part  of  the  sclerotic  6,  the  supra- 
choroid^ (pigmented)  lamellas  ;  !,  d,  the  layers 
of  the  choroid  coat ;  e,  the  pigmented  epithe- 
lium of  the  retina ;  f,  the  layer  of  rods ;  g,  the 
cones;  h,  the  layer  of  outer  nuclei ;  i,  the  outer 
molecular  layer ;  j,  the  layer  of  inner  nuclei ; 
k,  the  inner  molecular  layer ;  i,  the  layer  of 
ganglion  cells,  with  the  radial  or  MUller's 
fibres  between  ;  m,  the  layer  of  nerve-fibres. 
(Atlas.) 


Chap.  XXXIX.] 


The  Retina. 


309 


435.  From  this  arrangement  is  excepted — (a)  the 
papilla  nervi  optici,  (b)  the  macula  lutea  and  fovea 
centralis  retinae,  and  (c)  the  ora  serrata  of  the  retina. 

(a)  The  papilla  nervi  optici,  or  the  blind  spot  of 


Fig.  158. — Diagram  of  the  Ner-    Fig.  159. — Diagram  of  the  Connective 
vous  Elements  of  the  Eetina.  Tissue  Substance  of  the  same. 

2,  Nerve-fibres ;  3,  ganglion  cells;  4,  inner  molecular  layer ;   5,  inner  nuclear 

layer;  6,  outer  molecular  layer;    7,  outer  nuclear  layer;    8,  the  membrana 

limitans  externa ;  9,  the  rods  and  cones.    (Max  Schultze.) 

the  retina,  represents  the  entrance  of  the  optic  nerve- 
fibres  into  the  retina ;  thence,  as  from  a  centre, 
they  spread  out  in  a  radiating  direction  into  the 
saucer-shaped  retina,  of  which  they  form  the  internal 


310  Elements  of  Histology.    [Chap,  xxxix. 

layer.  No  other  elements  of  the  retina  are  present  at 
the  papilla,  except  a  continuation  of  the  limitans 
interna.  At  the  papilla  nervi  optici  the  arteria  and 
vena  centralis  nervi  optici  also  enter,  and  spread 
out  with  their  branches  in  the  inner  layers  of  the 
retina.     A  large  lymph  space  is  also  found  there. 

(b)  The  macula  lutea  and  fovea  centralis  will  be 
considered  after  the  various  layers  of  the  retina  have 
been  described. 

(c)  At  the  ora  serrata  all  cellular  and  nuclear 
elements  of  the  retina — except  the  pigmented  epithe- 
lium— and  the  nerve-fibres,  come  to  an  end ;  but  the 
limitans  interna,  with  its  peculiar  radial  or  Muller's 
fibres,  is  continued  over  the  ciliary  processes  in  the 
shape  of  columnar  epitheloid  nucleated  cells  men- 
tioned above  :  this  is  the  pars  ciliaris  retinae. 

436.  Structure  of  the  layers  of  the  retina  (Figs. 
158,  159). 

(1)  The  membrana  limitans  interna  is 
composed  of  more  or  less  polygonal  areas,  which  are 
the  ends  or  bases  of  pyramidal,  finely-striated  fibres 
— the  radial  fibres  of  Muller.  Each  radial  fibre  passes 
from  the  limitans  interna  in  a  vertical  direction 
through  all  layers  to  the  limitans  externa,  and  on  its 
way  gives  off  numerous  lateral  branchlets,  fibrils,  and 
membranes,  which  anastomose  with  one  another  so  as 
to  form  a  honeycombed  stroma  or  matrix  for  all 
cellular  and  nuclear  elements  of  the  retinal  layers. 
In  the  nerve-fibre  layer  the  radial  fibres  are  thickest, 
this  being,  in  fact,  the  pyramidal  basis  ;  in  the  inner 
nuclear  layer  each  possesses  an  oval  nucleus. 

437.  (2)  The  layer  of  nerve -fiores.— The 
optic  nerve-fibres  at  their  entrance  into  the  eyeball 
lose  their  medullary  sheath,  and  only  the  transparent 
axis  cylinder  is  prolonged  into  the  retina.  In  man, 
medullated  nerve-fibres  in  the  retina  are  very  excep- 
tional ;  in  the  rabbit  there  are  two  bundles,  whose 


Chap,  xxxix.]  The  Retina.  311. 

fibres  retain  their  medullary  sheath  in  the  retina 
(Bowman).  The  nerve-fibres  remain  grouped  in 
bundles  in  the  retina,  and  even  form  plexuses.  For 
obvious  reasons,  the  number  of  nerve-fibres  in  the 
nerve-fibre  layer  diminishes  towards  the  ora  serrata. 

438.  (3)  The  layer  of  ganglion  cells. — There 
is  one  stratum  of  these  cells  only,  except  in  the 
macula  lutea,  where  they  form  several  strata.  Each 
cell  is  multipolar,  and  possessed  of  a  large  nucleus. 
One  process  is  directed  inwards  and  becomes  con- 
nected with  a  fibre  of  the  nerve-fibre  layer.  Several 
processes  pass  from  the  opposite  side  of  the  cell,  and 
enter  the  next  outer  layer,  i.e.,  the  inner  molecular 
layer. 

According  to  Max  Schultze  and  others,  they  break 
up  there  into  a  reticulum  of  fibrils  which  is  part  of 
this  molecular  layer ;  but  according  to  Retzius,  Mans, 
and  Schwalbe,  they  simply  pass  through  the  inner 
molecular  layer. 

The  ganglion  cells  are  separated  from  one  another 
by  the  radial  fibres  of  Muller. 

439.  (4)  The  inner  molecular  layer  is  a 
fine  and  dense  reticulum  of  fibrils,  with  a  small 
amount  of  granular  matter  between.  The  fibrils  are 
connected  with  lateral  branchlets  of  the  radial  fibres 
of  Muller.  This  layer  is,  on  account  of  its  thickness, 
a  conspicuous  part  of  the  retina.  In  lower  vertebrates 
it  appears  stratified. 

440.  (5)  The  inner  nuclear  layer  contains  in 
a  honeycombed  matrix  of  a  hyaline  stroma  numerous 
nuclei,  in  two,  three,  or  four  layers.  In  the  am- 
phibian retina  these  form  a  larger  number  of  layers. 
Some  oblong  nuclei  of  this  layer  belong,  as  has  been 
mentioned  above,  to  the  radial  fibres  of  Muller. 
Next  to  the  molecular  layer  are  small  nuclei  belonging 
to  flattened  branched  cells  (Vintschgau).  But  the 
great  majority  of  the  nuclei  of  this  layer  are  slightly 


312  Elements  of  Histology.    [Chap,  xxxix. 

oval,  with  a  reticulum  in  their  interior.  Each  belongs 
to  a  spindle-shaped  cell,  with  a  small  amount  of  proto- 
plasm around  the  nucleus ;  it  is,  in  fact,  a  bipolar  gang- 
lion cell  (Max  Schultze),  of  which  one  process  (the 
inner)  passes  as  a  fine  varicose  fibre  into  and  through 
the  inner  molecular  layer,  to  become  connected  with 
the  outer  processes  of  the  ganglion  cells  (Retzius, 
Schwalbe),  while  the  other  or  outer  process  passes  into 
and  through  the  next  outer  layer  of  the  retina. 

(6)  The  outer  molecular  layer  is  of  exactly 
the  same  structure  as  the  inner  molecular  layer — i.e., 
a  fine  reticulum  of  fibrils — but  is  considerably  thinner 
than  the  latter. 

441.  (7)  The  outer  nuclear  layer  contains,  in 
a  honeycombed  matrix,  a  large  number  of  oval  nuclei. 
In  the  retina  of  man  and  mammals  these  nuclei  are 
always  present  in  considerably  greater  numbers  or 
layers  than  those  of  the  inner  nuclear  layer,  but  in 
the  amphibian  animals  the  reverse  is  the  case.  They 
are  smaller  than  the  nuclei  of  the  inner  nuclear  layer, 
and  show  often  a  peculiar  transversely-ribbed  differ- 
entiation of  their  contents  (Henle,  Krause).  The 
honeycombed  matrix  of  this  layer  is  in  connection 
with  lateral  branch]  ets  of  the  radial  fibres  of  Muller, 
with  which  it  forms  a  sort  of  limiting  delicate  mem- 
brana  propria  at  the  outer  surface  of  the  layer ; 
this  is 

442.  (8)  The  limit  an  s  externa. — The  nuclei  of 
the  outer  nuclear  layer  next  to  this  limitans  externa  are 
connected,  in  the  retina  of  man  and  mammals,  with 
the  cones,  while  the  nuclei  farther  inwards  from  the 
limitans  externa  are  connected  with  the  rods.  In 
both  instances  the  connection  is  established  through 
holes  in  the  limitans  externa.  Each  nucleus  of 
the  outer  nuclear  layer  is,  in  reality,  that  of  a 
spindle-shaped  cell  with  a  minute  amount  of  proto- 
plasm ;  this  is  prolonged  outwards,  as  the  outer  part 


Chap,  xxxix.]  The  Retina.  313 

of  the  rod-  or  cone-fibre,  to  become  connected  with  a 
rod  or  cone  respectively,  while  inwards  it  passes  into 
a  longer,  more  conspicuous  fibre,  the  inner  part  of  the 
rod-  or  cone-fibre.  This  branches,  and  penetrating 
into  the  outer  molecular  layer,  is  lost  with  its 
branchlets  among  the  fibrils  of  this  layer. 

443.  (9)  The  rods  and  cones. —  Each  rod  is 
of  cylindrical  shape,  with  rounded  or  conical  outer 
extremity ;  it  consists  of  an  outer  and  inner  member, 
joined  by  linear  cement.  Its  substance  is  bright  and 
glistening,  and  that  of  the  outer  member  is  composed 
of  the  neurokeratin  of  Kiihne  and  Ewald.  In 
the  fresh  state  the  outer  member  shows  a  more  or 
less  fine  and  longitudinal  striation,  due  to  longitudinal 
fine  ridges  and  furrows  (Hensen,  Max  Schultze). 
After  certain  reagents,  such  as  serum,  liquor  potassse, 
the  outer  rod-member  disintegrates  into  numerous 
transverse,  thin,  homogeneous-looking  discs  (Hannover). 
The  inner  member  in  the  human  rods  is  slightly 
broader  than  the  outer ;  it  is  pale  or  finely  and  longi- 
tudinally striated,  and  contains  in  many  instances  a 
peculiar  lenticular  structure ;  in  the  human  and 
mammalian  retina  this  is  absent,  but  in  its  stead  is  a 
mass  of  longitudinal  fibrils  (Max  Schultze).  The 
inner  member  passes  through  a  hole  in  the  limitans 
externa,  and  becoming  thinner,  represents  the  outer 
part  of  the  rod-fibre. 

444.  Each  cone  is  composed  of  an  outer,  short, 
pointed,  conical  member,  and  an  inner  larger  member 
with  convex  surface:  this  is  the  body  of  the  cone. 
The  outer  member  of  the  cone  separates  under  certain 
conditions  also  into  thin  transverse  discs.  The  body 
of  the  cone  is  longitudinally  and  finely  striated. 
The  outer  extremity  of  the  body  of  the  cones  in 
many  birds,  reptiles,  and  amphibia  contains  a  spheri- 
cal corpuscle  of  red,  orange,  yellow,  green,  or  even 
blue  colouration. 


3*4 


Elements  of  Histology.    [Chap,  xxxix. 


The  cones  are  shorter  than  the  rods,  the  pointed 
end  of  the  former  not  reaching 
much  farther  than  the  junction 
between  the  outer  and  inner 
members  of  the  rods. 

In  the  macula  lutea  and 
fovea  centralis  of  man  and 
most  mammals  there  are  pre- 
sent cones  only,  and  towards 
the  peripheral  portion  of  the 
retina  they  gradually  de- 
crease in  numbers;  in  the 
peripheral  part  there  are  only 
rods.  But  in  birds  the  cones 
exceed  the  rods  everywhere. 

In  the  bat  and  mole  the 
macula  lutea  possesses  no 
cones,  and  in  the  owl,  rat, 
mouse,  guinea-pig,  and  rabbit, 
they  are  few  and  small. 

445.  The  outer  members 
of  the  rods  (only)  contain  in 
the  fresh  and  living  state  a 
peculiar  diffuse  purplish  colour 
(Ley dig,  Boll,  Kuhne)  :  this 
is  the  visual  purple  or  Rhod- 
opsin  of  Kuhne.  When 
exposed  to  sunlight  it 
passes  through  red,  orange, 
and  yellow,  and  finally 
disappears  altogether  —  be- 
comes bleached.  There  is 
no  visual  purple  in  the  rods 
of  Rhinolof>hus  hipposideros, 
fowl  and  pigeon ;  in  those 
retinae  in  which  the  cones 
contain  coloured  globules  (see 


Fig.  160.— Vertical 
through,  the  Frog's  Eetina. 

x,  The  pigmented  epithelium 
of  the  retina  or  tapetum 
nigrum ;  6,  the  outer  mem- 
bers of  the  rods,  those  of 
cones  between  them  ;  c,  the 
inner  members  of  the  rods 
and  cones;  d,  limitans  ex- 
terna ;  e,  the  outer  nuclei ;  /, 
the  outer  molecular  layer;  g, 
the  inner  nuclei ;  h,  the  inner 
molecular  layer  ;  i,  the  nuclei 
of  the  ganglion  cells  ;  j,  the 
nerve-fibres ;  the  pyramidal 
extremities  of  the  radial 
fibres  are  well  shown.  (Atlas.) 


Chap,  xxxix.]  The  Retina.  315 

above)  the  surrounding  rods  are  wanting  in  the  visual 
purple. 

The  visual  purple  stands  in  an  intimate  relation  to 
the  pigmented  epithelium  of  the  retina,  since  a 
retina  regains  its  visual  purple  after  bleaching,  when 
replaced  on  the  pigmented  epithelium  (Kiihne).  This 
holds  good,  of  course,  only  within  certain  limits. 

446.  (10)  The  pigmented  epithelium  (Fig. 
160),  or  tapetum  nigrum,  is  composed  of  polygonal  pro- 
toplasmic cells,  which,  when  viewed  from  the  surface, 
appear  as  a  mosaic,  in  which  they  are  separated  from 
one  another  by  a  thin  layer  of  cement  substance.  Each 
cell  shows  an  outer  non-pigmented  part,  containing  the 
slightly-flattened  oval  nucleus,  and  an  inner  part  next  to 
the  rods  and  cones,  which  is  full  of  pigmented  crystalline 
rods  (Frisch).  This  part  is  prolonged  into  numerous 
fine  fibrils,  each  containing  a  row  of  the  pigmented 
particles,  and  these  fibrils  pass  between  the  outer 
members  of  the  rods,  to  which  they  closely  adhere,  and 
which  in  reality  become  almost  entirely  ensheathed 
in  them  (M.  Schultze).  Each  cell  supplies  a  number 
of  rods  with  these  fibrils.  Sunlight  causes  a  protru- 
sion of  these  fibrils  from  the  cell  body,  whereas  in 
the  dark  they  are  retracted  (Kiihne),  in  a  manner 
similar  to  what  takes  place  in  pigmented  connective 
tissue  cells.  (See  par.  43.)  The  tint  of  this  pigment 
is  darker  in  dark  than  in  light  eyes.  It  is  bleached 
by  the  light  in  the  presence  of  oxygen  (Kuhne),  but 
it  persists  in  the  absence  of  oxygen  (Mays). 

447.  The  macula  lutea  (Fig.  161)  of  man  and 
ape  contains  a  diffuse  yellow  pigment,  between  the  ele- 
ments of  the  retina  (M.  Schultze).  In  man  and  most 
mammals,  as  mentioned  above,  there  are  hardly  any 
rods  here,  but  cones  only ;  these  are  longer  than  in 
other  parts,  and  in  the  fovea  centralis  they  are 
longest,  and,  at  the  same  time,  very  thin.  Since 
there  are  few  rods  here,  the  nuclei  of  the  outer  nuclear 


316 


Elements  of  Histology.    [Chap,  xxxix. 


layer  are  limited  to  a  very  few  layers  (generally  about 
two)  next  to  the  membrana  liniitans  externa  For 
this  reason,  the  rest  of  the  outer  nuclear  layer  is 
occupied  by  the  cone-fibres  only,  which  in  the  fovea 
centralis    pass   in    a    slanting,    or    almost   horizontal, 


2    &- 


Pig.  161. — From  a  Vertical  Section  through,  the  Macula  Lutea  and 
Forea  Centralis. 

a,  Nerve-fibres;   6,  ganglion   cells:   c,  inner  molecular  layer;  d,  inner  nuclei; 
e,  oater  molecular  layer ;  /,  cone-fibres ;  g,  cones.    tDiagram  by  Mai  Scbultze.) 

direction  sideways  into  the  outer  molecular  layer. 
The  ganglion  cells  form  several  strata  in  the  macula 
lutea.  In  the  fovea  Centralis  are  present  the  cones 
(very  long  and  thin),  the  limitans  externa,  the  few 
auclei  representing  the  outer  nuclear  layer,  a  thin 
continuation  of  the  inner  molecular  layer,  and  the 
limitans  interna. 

-44  S.  In  the  embryo,  the  primary  optic  vesicle 
becomes  invaginated  so  as  to  form  the  optic  cup, 
which  consists  of  two  lavers — an  outer,  cnving  origin 
to  the  pigmented  epithelium  ;  and  an  inner,  the  retina 


Chap,  xxxix.]  The  Retina.  317 

proper.  In  this  the  rods  and  cones,  with  their  fibres 
and  the  nuclei  of  the  outer  nuclear  layer,  corre- 
spond to  columnar  epithelial  cells  (the  sensory  epithe- 
lium), while  all  the  other  layers — i.e.,  the  outer  mole- 
cular, inner  nuclear,  inner  molecular  layer,  ganglion 
cells,  nerve-fibres,  and  limitans  interna, — represent 
Briicke's  tunica  nervea  or  Henle's  stratum  nerveum. 

449.  The  blood-vessels  of  the  retina.  The 
branches  of  the  arteria  and  vena  centralis  of  the  optic 
nerve  can  be  traced  into  the  retina  in  the  layer  of 
nerve-fibres  and  ganglion-cells,  while  the  capillaries 
connecting  the  arteries  with  the  veins  extend  through 
the  layers  up  to  the  outer  molecular  layer. 

The  lymphatics  of  the  retina  exist  as  perivascular 
lymphatics  of  the  retinal  veins  and  capillaries  (His). 
Lymph  channels  are  present  in  the  nerve-fibre  layer. 

450.  The  lamina  cribrosa  is  the  part  of  the 
sclerotic  and  choroid  membrane  through  which  the  optic 
nerve-fibres  have  to  pass  in  order  to  reach  the  papilla 
nervi  optici.  In  the  optic  nerve  the  fibres  are  grouped 
in  larger  or  smaller  groups — not  bundles,  in  the  sense 
of  those  present  in  other  nerves  and  surrounded  by 
perineurium  (see  a  former  chapter) — but  surrounded 
by  septa  of  connective  tissue,  and  these  groups  pass 
through  corresponding  holes  of  the  sclerotic  and  choroid. 

451.  The  optic  nerve  possesses  three  sheaths, 
composed  of  fibrous  connective  tissue — (a)  an  outer, 
or  the  dural ;  (b)  a  middle,  or  arachnoidal ;  and  (c)  an 
inner,  or  pial,  sheath — which  are  continuations  of  the 
respective  membranes  of  the  brain.  The  pial  sheath 
is,  in  reality,  the  perineurium,  the  whole  optic  nerve 
being  comparable  to  a  compound  nerve-bundle  as  de- 
scribed in  a  former  chapter.  The  dural  sheath  of  the 
optic  nerve,  at  its  entrance  into  the  lamina  cribrosa, 
passes  into  the  outer  strata  of  the  sclerotic,  while  the 
arachnoidal  and  pial  sheaths  pass  into  the  inner  strata 
of  the  sclerotic.     Outside  the  dural  sheath  is  a  lymph 


318  Elements  of  Histology.        [Chap.  xl. 

space — the  supravaginal  space  ;  and  also  between  these 
various  sheaths  are  lymph  spaces — the  subdural  or 
subvaginal  space  of  Schwalbe,  and  the  subarachnoidal 
space.  The  supravaginal  and  subvaginal  spaces  anas- 
tomose with  one  another  (Michel). 

452.  Around  the  sclerotic  is  a  lymph  space  limited 
by  a  fibrous  membrane — the  Tenonian  capsule  :  the 
space  is  called  the  Tenonian  space.  The  supravaginal 
space  anastomoses  with  this  Tenonian  space,  and  into 
it  pass  also  the  lymph  clefts  in  the  suprachoroidal 
tissue  (Schwalbe),  by  means  of  the  lymph  canalicular 
system  of  the  sclerotic  (Waldeyer).  The  supracho- 
roidal lymph  spaces  communicate  also  with  the  sub- 
arachnoidal space  of  the  optic  nerve. 


CHAPTER   XL. 

THE    OUTER   AND    MIDDLE    EAR. 

453.  The  meatus  auditorius  externus  is  lined  with 
a  delicate  skin,  in  structure  identical  with,  but  thinner 
than,  the  skin  of  other  parts.  The  ceruminous 
glands  have  been  mentioned  and  described  before. 
The  cartilage  of  the  auricula  and  its  continuation  into 
the  meatus  auditorius  externus  is  elastic  cartilage. 

454.  The  membrana  tympani  separating  the 
outer  from  the  middle  ear  has  for  its  matrix  a  firm 
stratum  of  stiff  trabecule  of  fibrous  connective  tissue, 
with  numerous  elastic  fibrils  and  elastic  membranes. 
This  is  the  middle  and  chief  stratum  of  the  membrane  : 
outwards  it  is  covered  with  a  delicate  continuation  of 
the  skin  of  the  meatus  auditorius  externus,  and  inwards 
with  a  continuation  of  the  delicate  mucous  membrane 
lining  the  cavum  tympani.  In  the  middle  stratum  of 
the  membrana  tympani  the  trabecular  radiate  more  or 
less  from  the  junction  of  the  manubrium  mallei  with 
the  membrane ;  but  towards  the  periphery  many  are 


chap,  xl.]    The  Outer  and  Middle  Ear.  319 

also  arranged  in  a  circular  direction.  The  former 
belong  to  the  outer,  the  latter  to  the  inner,  portion  of 
the  middle  stratum. 

The  mucous  membrane  lining  the  tympanic  surface 
of  the  membrane  is  delicate  connective  tissue,  covered 
with  a  single  layer  of  polyhedral  epithelial  cells. 

The  blood-vessels  form  capillary  networks  for  all 
three  layers — i.t.,  sl  special  network  for  the  skin 
layer,  a  second  for  the  middle  stratum,  and  a  third  one 
for  the  mucous  layer  ;  the  lymphatics  are  also  arranged 
in  this  way.  An  intercommunicating  system  of  lym- 
phatic sinuses  and  clefts  (Kessel)  is  left  between  the 
trabecule.  The  non-medullated  nerve-fibres  form 
plexuses  for  the  skin  and  mucous  layer ;  from  these 
pass  off  fine  fibrils,  which  form  a  sub-epithelial  net- 
work, and  from  this  the  fibrils  pass  into  the  epithelium. 

455.  The  tuba  ~Eiistachii  is  lined  with  a 
mucous  membrane,  which  is  a  continuation  of  that 
lining  the  upper  part  of  the  pharynx,  and  therefore, 
like  it,  is  covered  on  its  inner  or  free  surface  with 
columnar  ciliated  epithelium.  As  in  the  pharynx,  so 
also  here,  we  find  a  good  deal  of  adenoid  tissue  in  the 
mucous  membrane. 

The  cartilage  of  the  tuba  Eustachii  in  the  adult  ap- 
proaches in  structure  the  elastic  cartilages  of  other  parts. 

4:56.  The  cavuni  tympani,  including  the  cellulse 
mastoidese  and  the  surface  of  the  ossicula  auditus,  is 
lined  with  a  delicate  connective  tissue  membrane.  Its 
free  surface  is  covered  with  a  single  layer  of  poly- 
hedral epithelial  cells  in  the  following  regions  :  on 
the  promontory  of  the  inner  wall  of  the  cavity,  on  the 
ossicula  auditus,  on  the  roof  of  the  cavity,  and  in  the 
cellulse  mastoideae ;  in  all  other  parts  it  is  columnar  cili- 
ated epithelium,  like  that  lining  the  tuba  Eustachii. 

457.  The  three  ossicula  auditus  are  osseous 
substance  covered  with  periosteum,  which  is  covered 
with  the  delicate  mucosa  just  described.     The  liga- 


320  Elements  of  Histology.       [Chap.  xli. 

ments  of  the  bones  are,  like  other  ligaments,  made  up 
of  straight  and  parallel  bundles  of  fibrous  connective 
tissue.  The  articulation  surface  of  the  head  of  the 
malleus,  of  the  incus,  of  the  extremity  of  the  long 
process  of  the  incus,  and  of  the  stapes,  are  covered 
with  hyaline  (articular)  cartilage. 


CHAPTER    XLI. 

THE     INTERNAL     EAR. 

458.  The  osseous  labyrinth  consists  of  the  vesti- 
bule, prolonged  on  one  side  into  the  cochlea,  and  on 
the  other  into  the  three  semicircular  canals,  each  of 
which  possesses  an  ampulla  at  one  extremity.  The 
vestibule  shows  two  divisions — the  fovea  hemispherica 
next  to  the  cochlea,  and  the  fovea  hemielliptica  next 
to  the  semicircular  canals.  The  cochlea  consists  of 
two  and  half  turnings  twisted  round  a  bony  axis — the 
modiolus.  From  this  a  bony  lamina  extends  towards 
the  outer  wall  for  each  turn,  but  does  not  reach  it : 
this  is  the  lamina  spiralis  ossea.  It  extends  through 
all  turns,  and  it  subdivides  the  cavity  of  each  turn 
into  an  upper  passage,  or  scala  vestibuli,  and  a  lower, 
or  scala  tympani.  At  the  top  of  the  cochlea  the  two 
scalse  pass  into  one  another  by  the  helicotrema.  The 
scala  vestibuli  opens  into  the  fovea  hemispherica, 
while  the  scala  tympani  at  its  commencement — i.e., 
at  the  proximal  end  of  the  first  turn — would  be  in 
communication,  by  the  fenestra  rotunda,  with  the 
cavum  tympani,  were  it  not  that  this  fenestra  rotunda 
is  closed  by  a  membrane — the  secondary  membrane. 

459.  The  semicircular  canals  start  from,  and  return 
to,  the  fovea  hemielliptica  of  the  vestibule. 

The  fenestra  ovalis  leads  from  the  cavum  tympani 
into  the  vestibule — its  hemispheric  division ;  and  this 


Chap,  xll]  The  Internal  Ear.  321 

fenestra  ovalis  is,  in  the  fresh  condition,  filled  out  by  a 
membrane,  in  which  the  basis  of  the  stapes  is  fixed, 
the  circumference  of  this  being  nearly  as  great  as  that 
of  the  fenestra. 

460.  The  osseous  labyrinth  in  all  parts  consists  of 
ordinary  osseous  substance,  with  the  usual  periosteum 
lining  its  outer  surface  and  its  inner  cavities.  These 
cavities  contain  the  albuminous  fluid  called  perilymph. 
But  they  are  not  filled  out  by  this,  since,  in  each  of 
the  two  divisions  of  the  vestibule,  in  each  of  the 
semicircular  canals,  and  in  the  cochlea,  is  a  mem- 
branous structure,  analogous  in  shape  to  the  corre- 
sponding division  of  the  labyrinth.  These  membranous 
structures  possess  a  cavity  filled  with  the  same  albu- 
minous fluid  as  above,  called  the  endolymph.  These 
structures  are  disposed  thus — in  the  fovea  hemispherica 
is  a  spherical  sac,  called  the  saccule ;  in  the  fovea 
hemielliptica  is  an  elliptical  sac,  the  utricle;  in  each  of 
the  three  semicircular  canals  is  a  membranous  semi- 
circular tube,  which  possesses  also  an  ampulla  corre- 
sponding to  the  ampulla  of  the  bony  canal. 

461.  In  the  cochlea  is  a  membranous  canal,  tri- 
angular in  cross-section — the  scala  media  or  cochlear 
duct — which  also  twists  two  and  half  times  from  the 
basis  to  the  apex  of  the  cochlea,  and  is  placed  against 
the  end  of  the  lamina  spiralis  ossea  so  as  to  occupy  a 
position  between  the  peripheral  part  of  the  scala  vesti- 
buli  and  scala  tympani. 

462.  The  different  divisions  of  the  membranous 
labyrinth  are  connected  with  one  another  in  this 
manner  :  the  three  semicircular  (membranous)  canals 
open  into  the  utricle ;  this  does  not  form  a  direct  con- 
tinuity with  the  saccule,  but  a  narrow  canal  comes  off 
both  from  the  saccule  and.  utricle ;  the  two  canals 
join  into  one  minute  membranous  tube  situated  in  the 
aqueductus  vestibuli.  At  its  distal  end  it  enlarges 
into  the  saccus  endolymphaticus,  situated  in  a  cleft  of 

v 


322  Elements  of  Histology.       [chap.  xli. 

the  dura  mater,  covering  the  posterior  surface  of  the 
petrous  bone.  The  saccule  is  in  communication  with 
the  cochlear  canal  or  scala  media,  by  a  short  narrow 
tube — the  canalis  reuniens  of  Reichert.  Thus  the 
cavity  of  the  whole  membranous  labyrinth  is  in 
direct  communication  throughout  all  divisions,  and  it 
represents  the  inner  lymphatic  space  of  the  labyrinth. 
There  is  no  communication  between  the  perilymph 
and  endolymph,  and  the  cavity  of  the  membranous 
labyrinth  stands  in  no  direct  relation  to  the  cavum 
tympani,  since  the  fenestra  ovalis  and  fenestra  rotunda 
both  separate  the  perilymphatic  space,  or  the  cavity 
of  the  bony  labyrinth,  from  the  cavum  tympani.  The 
vibrations  of  the  membrana  tympani,  transferred  by 
the  ossicula  auditus  to  the  fenestra  ovalis,  directly 
affect,  therefore,  only  the  perilymph.  The  fluctuations 
of  this  pass  from  the  vestibule,  on  the  one  side, 
towards  and  into  the  perilymph  of  the  semicircular 
canals ;  and  on  the  other  side,  through  the  scala 
vestibuli,  to  the  top  of  the  cochlea,  then  by  the  heli- 
cotrema  into  the  scala  tympani,  and  find  their  conclu- 
sion on  the  membrana  secundaria  closing  the  fenestra 
rotunda.  On  their  way  they  affect,  of  course,  the 
membrane  of  Reissner  (see  below)  separating  the  scala 
media  from  the  scala  vestibuli ;  and  the  vibrations  of 
this  membrane  naturally  affect  the  endolymph  of  the 
scala  media  and  the  terminations  of  the  auditory 
nerve-fibres  (see  below). 

463.  Structure  of  semicircular  canals, 
utricle  and.  saccule. — The  membranous  semi- 
circular canals  are  fixed  by  stiff  bands  of  fibrous 
tissue  to  the  inner  periosteum  of  the  one  (convex) 
side  of  the  osseous  canal,  so  that  towards  the  concave 
side  there  is  left  the  space  for  the  perilymph.  A 
similar  condition  obtains  with  regard  to  the  saccule 
and  utricle,  which  are  fixed  by  the  inner  periosteum 
to  one  side  of  the  bony  part. 


Chap.XLI.] 


The  Internal  Ear. 


323 


The  structure  of  the  wall  is  the  same  in  the  semi- 
circular canals,  utricle  and  saccule.  The  above-men- 
tioned fibrous  ligaments  of  the  periosteum  form  an 
outer  coat;  inside  this  is  a  glassy- looking  tunica 
propria.  At  one  side  (the  one  away  from  the  bone) 
this  tunica  propria  forms  numerous  papillary  projec- 
tions. The  internal 
surface  of  the  mem- 
brane is  covered  with  a 
single  layer  of  poly- 
hedral epithelial  cells. 

464.  Each  of  the 
branches  of  the  nervus 
vestibuli — i.e.,  one  for 
the  saccule,  one  for  the 
utricle,  and  three  for 
the  three  ampullse— 
possesses  a  ganglionic 
swelling.  The  nerve- 
branch,  having  passed 
through  the  membra- 
nous wall,  enters 
special  thickenings  of 
the  tunica  propria,  on 
that  part  of  the  mem- 
branous wall  next  to 
the  bone ;  in  the  sac- 
cule and  utricle  the 
thickening  is  called 
macula  acustica,  in  the 
ampullee  crista  acustica 

(Fig.  162)  (M.  Schultze).  This  thickening  is  a  large 
villous  or  fold-like  projection  of  the  tunica  propria, 
into  which  pass  the  nerve-fibres  of  the  several 
branches.  These  fibres  are  all  medullated  nerve- 
fibres,  and,  ascending  towards  the  internal  or 
free  surface  of  that  projection,   form  a  plexus.     In 


Fig.  162.— From  a  Transverse  Section 
through  the  Macula  Acustica  of  the 
Utricle  of  the  Labyrinth  of  a  Guinea- 
pig. 

a,  Medullated  nerve  fibres,  forming  plex- 
uses ;  6,  nuclei  of  the  membrane ;  c, 
the  sensory  epithelium  fdiagramruatirl ; 
the  spindle-shaped  sensory-cells  possess 
long  auditory  hairs_  projecting  between 
the  conical  epithelial  cells  heyond  the 
free  surface.    (Atlas.) 


324  Elements  of  Histology.      [Chap.  xli. 

this  plexus  are  interspersed  numerous  nuclei.  From 
the  medullated  fibres  pass  off  minute  bundles  of 
primitive  fibrillse,  which  enter  the  epithelium  that 
covers  the  free  surface  of  the  projection. 

465.  This  epithelium  is  composed  of  a  layer  of 
columnar  or  conical  cells,  between  which  are  wedged 
in  spindle-shaped  cells ;  both  kinds  possess  an  oval 
nucleus.  According  to  Max  Schultze  and  others,  each 
of  the  spindle-shaped  cells  is  connected  by  its  inner 
process  with  the  nerve-fibrillse  coming  from  under- 
neath ;  whereas,  towards  and  beyond  the  free  surface, 
its  outer  process  is  prolonged  into  a  long,  thin,  stiff', 
auditory  hair.  Max  Schultze,  therefore,  calls  the 
columnar  cells  epithelial;  the  spindle-shaped  ones, 
sensory. 

Retzius,  on  the  other  hand,  maintains  that,  in  the 
case  of  fishes  at  any  rate,  the  epithelial  cells  are  those 
which  are  connected  each  with  a  bundle  of  nerve- 
fibrillse,  and  that  each  sends  out  over  the  internal  free 
surface  a  bundle  of  fine  stiff  hairs — the  auditory  hairs. 
The  spindle-shaped  cells  of  Max  Schultze,  according 
to  this  theory,  are  only  supporting  cells.  The  free 
surface  of  the  epithelium  is  covered  with  a  homo- 
geneous cuticle,  perforated  by  holes  which  correspond 
to  the  epithelial  cells  and  the  auditory  hairs. 

On  the  internal  surface  of  the  macula  and  crista 
acustica  are  found  the  otoliths,  rhombic  crystals,  and 
amorphous  masses,  chiefly  of  carbonate  of  lime,  em- 
bedded in  a  gelatinous  or  granular-looking  basis. 

466.  The  cochlea  (Fig.  163),  as  has  been  men- 
tioned above,  consists  also  of  a  bony  shell  and  a 
membranous  canal,  the  former  surrounding  the  latter 
in  the  same  way  as  the  bony  semicircular  canal  does 
the  membranous — i.e.,  the  latter  is  fixed  to  the  outer 
or  convex  side  of  the  former.  The  difference  between 
the  cochlea  and  the  semicircular  canals  is  this,  that  in 
the  cochlea  there  is  a  division  of  the  perilymphatic 


Chap.  XLL] 


Fig.  163. — From  a  Vertical  Section  through  the  Cochlea  of  a  Guinea- 
pig's  Ear,  seen  in  the  long  axis  of  the  Modiolus. 

a,  The  scala  vestibuli ;  6,  the  scala  tynipani ;  c,  the  scala  media ;  d,  the  membrana 
tectoria ;  e,  the  cells  of  Claudius ;  /,  the  upper  outer  angle  of  the  scala  media  : 
g,  the  region  of  the  outer  hair  cells  on  the  membrana  hasilaris  ;  h,  the  mem- 
brane of  Reissner ;  i.  the  epithelium  lining  tne  sulcus  spiralis  (jnternus)  ;/,  the 
tunnel  of  Corti's  arch;  k  the  stria  vascularis;  I,  the  lignmentum  spirale ; 
vi,  the  crista  spiralis;  n,  the  nerve-fibres  in  the  lamina  spiralis  ossea  ;  o,  the 
ganglion  spirale  ;  p,  the  nerve-fibres  in  the  modiolus  ;  q,  channels  in  bone  con- 
taining blood-vessels  ;  r,  masses  of  bone  in  the  modiolus  ;  s,  the  bony  capsule. 
(Atlas.) 


326  Elements  of  Histology.       [Chap.  xli. 

space  by  an  osseous  projection— -the  lamina  spiralis 
ossea — and  by  the  scala  media  into  two  scalse,  viz.,  the 
(upper)  scala  vestibuli,  and  the  (lower)  scala  lympani. 

467.  In  the  osseous  modiolus  are  numerous  paral- 
lel canals  for  bundles  or  groups  of  the  fibres  of  the 
cochlear  branch  of  the  auditory  nerve ;  these  canals 
open  into  the  porus  internus,  in  which  lies  a  large 
ganglion  connected  with  the  nerve. 

The  nerve  bundles  situated  in  the  canals  of  the 
modiolus,  corresponding  to  the  lamina  spiralis  ossea, 
are  connected  with  ganglionic  masses- — composed  of 
bipolar  ganglion  cells — called  the  ganglion  spirale  of 
Corti.  From  this  ganglionic  mass  the  nerve-fibres  (all 
medullated)  can  be  traced  into  the  lamina  spiralis 
ossea,  in  which  they  form  rich  plexuses  extending  to 
the  margin  of  this  lamina — i.e.,  to  the  membrana 
basilaris  of  the  scala  media  (see  below). 

468.  From  the  margin  of  the  lamina  spiralis  ossea 
to  the  external  bony  shell  extends  the  membrana  basi- 
laris (Fig.  163),  forming  the  lower  and  chief  wall  of 
the  scala  media,  while  the  upper  wall  of  the  canal  is 
formed  by  the  membrane  of  Reissner,  extending 
under  an  acute  angle  from  near  the  margin  of  the 
lamina  spiralis  ossea  to  the  outer  bony  shell. 

On  a  transverse  section  through  the  scala  media 
we  see  the  following  structures  :— 

469.  (1)  Its  outer  wall  is  placed  close  against 
the  periosteum  lining  the  internal  surface  of  the  bony 
shell ;  it  consists  of  lamellar  fibrous  tissue,  with 
numerous  stiff  elastic  bands,  and  is  the  vestibular 
part  of  a  peculiar  ligament — the  ligamentum  spirale 
(Kolliker)— semi-lunar  in  cross  section,  and  with  its 
middle  angular  projection  fixed  to  the  outer  end  of 
the  membrana  basilaris. 

470.  (2)  Its  inner  wall  is  represented  by  an 
exceedingly  delicate  membrane — the  membrane  of 
Reissner  ;  this  is  also  its  upper  wall,  extending  under 


chap,  xll]  The  Internal  Ear.  327 

an  acute  angle  from  the  upper  outer  angle  of  the  scala 
media  to  the  lamina  spiralis  ossea.  But  there  it  is  not 
fixed  on  the  osseous  substance,  but  on  a  peculiar  pro- 
jection on  this  latter — the  crista  spiralis  (Fig.  163,  m), 
which  is  a  sort  of  tissue  intermediate  between  fibrous 
and  osseous  tissue,  and  added  to  the  vestibular  surface 
of  the  lamina  spiralis  ossea.  This  crista  spiralis  has 
on  its  inner  surface — i.e.,  that  directed  towards  the 
scala  media — a  deep  sulcus,  called  the  sulcus  spiralis,  or 
sulcus  spiralis  internus ;  so  that  of  the  crista  spiralis 
there  are  two  labia  to  be  distinguished — the  labium 
vestibulare  and  the  labium  tympanicum;  the  former 
being  the  upper,  the  latter  the  lower,  boundary  of  the 
sulcus  spiralis. 

471.  (3)  Between  the  labium  tympanicum  of  the 
crista  spiralis  and  the  above-mentioned  projection 
of  the  ligamentum  spirale  extends,  in  a  straight 
direction,  the  membrana  basilaris,  forming  the  lower 
wall  of  the  scala  media.  The  scala  media  is  lined  on 
its  whole  internal  surface  with  epithelium,  this  only 
being  derived  from  the  epithelium  forming  the  Avail  of 
the  auditory  vesicle  of  the  embryo,  peculiarly  modified 
in  certain  places.  The  scala  tympani  and  scala  vesti- 
buli  are  likewise  lined  with  a  continuous  layer  of 
flattened  cells — an  endothelium,  which  only  on  the 
lower  (tympanic)  surface  of  the  membrana  basilaris 
is  somewhat  modified,  being  composed  of  granular 
looking  irregular  cells. 

472.  As  regards  the  scala  media,  the  epithelium 
lining  its  internal  surface  is  of  the  folllowing  aspect  : 
Starting  with  the  lower  outer  angle — i.e.,  where  the 
membrana  basilaris  is  fixed  to  the  ligamentum 
pirale — we  find  it  a  single  layer  of  polyhedral  or 
short  columnar  transparent  cells,  lining  this  outer 
angle — the  cells  of  Claudius  ;  ascending  on  the  liga- 
mentum spirale,  the  cells  become  shorter,  more  squa- 
mous ;   such  are   found   over  a  slight  projection  on 


328  Elements  of  Histology.       [Chap.  xli. 

the  outer  wall — i.e.,  the  ligamentum  spirale  accesso- 
rium — caused  by  a  small  blood-vessel,  the  vas  pro- 
niinens. 

473.  Then  we  come  to  the  stria  vascularis, 

lining  nearly  the  upper  two-thirds  of  the  outer 
wall  of  the  scala  media.  It  consists  of  a  layer  of 
columnar  and  spindle-shaped  epithelial  cells,  between 
which  extend  capillary  blood-vessels  from  the  ligamen- 
tum spirale,  and  in  some  animals  (guinea-pig)  clumps 
of  pigment  granules  are  found  between  them. 

474.  Then  we  pass  from  the  upper  angle  of  the  scala 
on  to  the  membrane  of  Reissner.  This  consists  of  a 
homogeneous  thin  membrana  propria,  covered  on  its 
outer  vestibular  surface  with  a  layer  of  flattened 
endothelium,  and  on  its  inner  surface — i.e.,  that  facing 
the  scala  media — with  a  layer  of  less  flattened,  smaller, 
polyhedral,  epithelial  cells. 

475.  We  come  next  to  the  vestibular  labium  of 
the  crista  spiralis,  on  which  peculiar  cylindrical 
horizontal  projections  anastomose  with  one  another  : 
these  are  the  auditory  teeth  (Huschke).  The  epi- 
thelium of  Reissner 's  membrane  is  continued  as  small 
polyhedral  cells  into  the  grooves  and  pits  between  the 
auditory  teeth,  but  over  the  teeth  as  large,  flattened, 
squamous  cells,  which  pass  on,  lining  the  sulcus 
spiralis,  and,  as  such,  cover  also  the  tympanic  labium 
of  the  crista  spiralis.  Now  we  arrive  at  the  mem- 
brana basilaris,  on  which  the  epithelium  becomes 
modified  into  the  organ  of  Corti. 

476.  The  membrana  basilaris  consists  of  a 
hyaline  basement  membrane,  on  which  the  organ  of 
Corti  is  fixed  ;  underneath  this  is  the  tunica  propria, 
a  continuation  of  the  tissue  of  the  ligamentum  spirale, 
composed  of  fine  parallel  stiff  fibrils  (Hannover, 
Henle)  stretched  in  a  very  regular  and  beautiful 
manner  in  the  direction  from  the  ligamentum  spirale 
to  the  crista  spiralis  (Nuel).      On  the  tympanic  side 


Chap.  XLI.] 


The  Internal  Ear. 


329 


there  is  also  a  hyaline  basement  membrane.  The 
endothelial  cells  covering  this  on  the  tympanic  surface 
have  been  mentioned  above* 

477.  The  organ  of  Corti  (Fig.  164).— Passing 
outwards  from  the  epithelium  lining  the  sulcus  spiralis, 
we  meet  with  small  polyhedral  epithelial  cells  in  the 
region  of  the  termination  of  the  lamina  spiralis  ossea, 
next  which  are  columnar-looking  cells — the  inner" 
supporting  cells;  next  to  these  is  the  inner  hair-cell — 


Fig.  164. — Organ  of  Corti  of  the  Cochlea  of  a  Guinea-pig. 

a,  Outer  rod  or  pillar  of  Corti ;  b,  inner  rod  or  pillar  of  Corti ;  c,  tunnel  of  Corti's 
arch ;  d,  outer  hair-cells ;  e,  inner  hair-cell ;  /,  outer  supporting  cells  contain- 
ing fat  globules ;  g,  inner  supporting  cells;  h,  cells  of  Claudius;  i,  epithelial 
cells  lining  the  sulcus  spiralis  internus ; .?,  nerve-fibres;  k,  part  of  crista 
spiralis.    (Atlas.) 

a  columnar,  or  conical,  epithelial  cell,  with  a  bundle 
of  stiff  hairs,  or  rods,  extending  beyond  the  surface. 
The  inner  hair-cells  form  a  single  file  along  the  whole 
extent  of  the  two  and  a  half  turns  of  the  scala  media. 
478.  Next  to  the  inner  hair-cell  is  the  inner  rod,  or 
inner  pillar,  of  Corti,  and  next  to  this  the  outer  rod, 
or  outer  pillar,  of  Corti.  Each  forms  a  single  file  for 
the  whole  extent  of  the  two  and  a  half  turns  of  the 
scala  media.  The  two  rods  are  inclined  towards  one 
another,  and  in  contact  with  their  upper  extremity,  or 
head;  whereas  their  opposite  extremity,  the  foot, 
rests  under  an  acute  angle  on  the  membrana  basilaris, 
on  which  it  is  firmly  fixed.  The  rest  of  the  rod  is  a 
slender,  more  or  less  cylindrical,  piece — the  body.     The 


33°  Elements  of  Histology.       [Chap.  xli. 

outer  rod  is  larger  and  longer  than  the  inner,  the 
latter  being  slightly  bent  in  the  middle.  Owing  to 
the  position  of  the  rods,  the  two  files  form  an  arch — - 
the  arch  of  Corti.  Between  it  and  the  corresponding 
part  of  the  basilar  membrane  is  a  space — the  tunnel  of 
the  arch,  triangular  in  cross  section. 

479.  The  substance  of  the  rods,  or  pillars,  of  Corti 
is  bright,  highly  refractive,  and  slightly  and  longitu- 
dinally striated. 

The  head  of  the  inner  rod  is  triangular,  a  short 
process  extending  inwards  towards  the  inner  hair-cell, 
a  long  process  extending  outwards  over  the  head  of 
the  outer  pillar.  Outwards,  the  triangular  head  pos- 
sesses a  concave  surface  grasping  the  convex  surface  of 
the  head  of  the  outer  rod.  This  latter  possesses  a 
process  directed  outwards,  and  firmly  applied  to  the 
outer  process  of  the  head  of  the  inner  rod,  the  two 
together  forming  part  of  the  membrana  reticularis  (see 
be]ow). 

The  relation  between  the  outer  and  inner  rods  is 
such  that  the  head  of  one  outer  rod  fits  into  those  of 
about  two  inner  rods. 

480.  At  the  foot,  each  rod  has,  on  the  side  directed 
towards  the  tunnel,  a  granular,  nucleated,  lump  of 
protoplasm,  probably  the  remnant  of  the  epithelial 
cell  from  which  the  lower  half  of  the  rod  is  derived ; 
the  upper  part  sometimes  possesses  a  similar  remnant, 
proving  that  this  also  has  been  formed  by  an  epithelial 
cell,  so  that  each  rod  is  in  reality  derived  from  two 
epithelial  cells  (Waldeyer). 

481.  Next  follow  three  or  four  rows  of  outer  hair- 
cells,  similar  in  size  and  structure  to  the  inner  hair- 
cells.  Each  of  the  outer  hair-cells  represents  a  file 
of  hair-cells,  extending  on  the  membrana  basilaris 
along  the  whole  extent — i.e.,  two  and  a-half  turns — ■ 
of  the  scala  media.  Each  hair-cell  possesses  an  oval 
nucleus  and  a  number  of  stiff  rods,  or  hairs,  disposed 


chap,  xli.]  The  Internal  Ear.  331 

in  the  shape  of  a  horseshoe  in  the  outer  part  of  the 
free  surface  of  the  cell. 

Four,  and  even  five,  rows  of  hair-cells  (Waldeyer), 
arranged  in  an  alternating  manner,  are  found  in 
man. 

The  outer  hair-cells  are  also  called  the  cells  of 
Corti;  they  are  conical,  and  more  or  less  firmly  con- 
nected with  a  nucleated  spindle-shaped  cell — the  cell 
of  Deiters.  The  two  cells  are  more  or  less  fused 
together  in  their  middle  part  (Kuel).  The  cell  of 
Corti  is  fixpd  by  a  branched  process  to  the  membrana 
basilaris,  while  the  cell  of  Deiters  sends  a  process 
towards  the  surface,  where  it  joins  the  membrana 
reticularis  (see  below). 

482.  Farther  outwards  from  the  last  row  of  outer 
hair-cells  are  columnar  epithelial  cells,  called  the  outer 
supporting  cells  of  Hensen  ;  they  forru  the  transition 
to  the  epithelium  lining  the  outer  angle  of  the  scala 
media,  i.e.,  to  the  cells  of  Claudius. 

In  the  guinea-pig,  the  outer  supporting  cells  in- 
clude fat  globules. 

483.  The  medullated  nerve-fibres,  which  we 
traced  in  a  former  page  to  the  margin  of  the  lamina 
spiralis  ossea,  make  rich  plexuses  in  this,  and  pass 
through  holes  in  it,  in  order  to  reach  the  organ  of 
Corti  on  the  membrana  basilaris,  Looking  from  the 
surface  on  this  part,  we  notice  a  row  of  holes — the 
liabenula  perforata  of  Kblliker — a  little  to  the  inside 
of  the  region  of  the  inner  hair-cells.  Numerous 
primitive  fibrillar  pass  there  among  small  nucleated 
cells  situated  underneath  the  inner  hair-cells :  these 
are  the  granular  cells.  Some  of  these  nerve-fibrilla3 
— the  inner  bundle  of  spiral  nerve-fibx^es — become  con- 
nected with  the  inner  hair-cells ;  while  others — the 
three  outer  bundles  of  spiral  fibrils  (Waldeyer) — pass, 
between  the  inner  rods  of  Corti,  right  through  the 
tunnel ;  and,  further,  penetrating  between  the  outer 


332  Elements  of  Histology.       [Chap.  xli. 

rods  of   Corti,  they  reach  the    outer  hair-cells,  with 
which  they  become  connected  (G-ottstein,  Waldeyer). 

484.  In  connection  with  the  outer  process  of  the 
head  of  the  inner  and  outer  rods  of  Corti,  mentioned 
above,  is  an  elastic  hyaline  membrane — the  lamina 
or  membrana  reticularis.  It  extends  outwards  over 
the  organ  of  Corti  to  the  supporting  cells  of  Hensen, 
and  possesses  holes  for  the  tops  of  the  outer  hair-cells 
and  their  hairs.  The  parts  between  the  rods  of  Corti 
and  between  the  outer  hair-cells  appear  of  the  shape  of 
phalanges — phalanges  of  Deiters.  A  short  cuticular 
membrane  extends  from  the  head  of  the  inner  rod  of 
Corti  inwards  to  the  inner  supporting  cells  :  it  possesses 
holes  for  the  tops  of  the  inner  hair-cells. 

485.  From  the  Vestibular  labium  of  the  crista 
spiralis  to  the  outer  hair-cells  of  the  organ  of  Corti 
extends  a  peculiar  fibrillated  membrane — the  mem- 
brana tectoria.  By  means  of  it  the  sulcus  spiralis 
internus  is  bridged  over,  and  s6  converted  into  a 
canal. 

486.  As  we  ascend  towards  the  top  of  the  cochlea, 
all  parts  in  the  scala  media  decrease  gradually  in  size. 
The  organ  of  Corti,  being  of  an  epithelial  nature, 
possesses  no  blood-vessels.  From  the  anatomical 
relations  of  the  organ  of  Corti,  it  appears  most  pro- 
bable that  the  pillars,  or  rods,  of  Corti  act  as  the 
supporting  tissue,  or  framework,  around  which  the 
other  elements  are  grouped ;  and  it  seems  likely 
that  the  hair-cells,  with  their  rod-like  hairs  projecting 
freely  into  the  endolymph,  are  the  real  sound-perceiving 
elements  of  the  organ  of  Corti.  Their  connection 
with  the  terminal  nbrillse  of  the  nerves  points  in  the 
same  direction. 


Chap.  XLII.]  333 


CHAPTER   XLII. 

THE    NASAL    MUCOUS    MEMBRANE. 

487.  The  lower  part  of  the  nasal  cavity  is  lined 
with  a  mucous  membrane,  which  has  no  relation  to 
the  olfactory  nerve,  and  therefore  is  not  connected 
with  the  organ  of  smell.  It  is  covered  with  a  strati- 
fied, columnar,  ciliated  epithelium  of  exactly  the  same 
nature  as  that  of  the  respiratory  passages — e.g.,  the 
larynx  and  trachea.  Large  numbers  of  mucous  secret- 
ing goblet-cells  are  met  with  in  it.  Below  the  epi- 
thelium is  a  thick  hyaline  basement  membrane,  and 
underneath  this  is  a  mucosa  of  fibrous  tissue,  with 
numerous  lymph  corpuscles  in  it.  In  many  places  this 
infiltration  with  lymph  corpuscles  amounts  to  diffuse 
adenoid  tissue,  or  to  perfect  lymph  follicles. 

488.  The  mucosa  contains  in  its  most  superficial 
layer  the  network  of  capillaries,  but  in  the  rest  it 
includes  a  rich  and  conspicuous  plexus  of  venous 
vessels. 

In  the  deeper  parts  of  the  mucous  membrane — 
i.e.,  in  the  submucosa — are  embedded  smaller  and 
larger  glands,  the  ducts  of  which  pass  through  the 
mucosa,  and  open  on  the  free  surface.  Some  of  the 
glands  are  mucous ;  others  are  serous.  In  some  cases 
(e.g.,  guinea-pig)  almost  all  glands  are  serous,  and 
of  exactly  the  same  nature  as  those  of  the  back  of 
the  tongue.  In  some  places  the  mucous  membrane  is 
much  thicker  than  in  others,  and  then  it  contains 
larger  glands,  and  between  them  bundles  of  non-striped 
muscular  tissue. 

489.  In  the  upper  or  olfactory  region  (Fig.  165) 
of   the  nasal  cavity,   the  mucous  membrane  is  of   a 


334 


Elements  of  Histology.      [Chap.  xlti. 


different  tint,  being  more  of  a  brownish  colour  •  it 
contains  the  ramifications  of  the  olfactory  nerve,  and 
is  the  seat  of  tine  organ  of  smell. 

490.  The  free  surface  is  covered  with  a  columnar 


Fig.  165.— From  a  Section  through  the  Olfactory  Region  of  the 
Guinea-pig. 
«,  Thick  olfactory  epithelium ;   b,  thin   olfactory  epithelium!  e.  ciliated  non- 
olfactory  epithelium;  d,  hone.      The  transverse  sections  of  the  olfactory 
nerve  bundles  and  the  tubular  glands  of  Bowman  are  well  seen.    (Atlas.) 

epithelium,  composed  of  the  following  kinds  of  cells 
(Fig.  166):— 

(a)  A  superficial  layer  of  long  columnar,  or  rather 


chap,  xlil]    Nasal  Mucous  Membrane. 


335 


conical,  epithelial  cells,  each  with  an  oval  nucleus.  In 
some  places  the  free  surface  of  these  cells  is  covered 
with  a  bundle  of  cilia,  similar  to  the  superficial  cells 

JIJJlUlJJJlU  1  4  Hi  I  >"  1 1  l!i  I 


*IM 


Fig.  166.— From  a  Vertical  Section  through  the  Olfactory  Mncotta 
Membrane  of  the  Guinea-pig. 
a,  The  epithelial  cells;  6,  the  sensory  or  olfactory  cells;  c,  the  deep  epithelial 
cells ;   d,  the  bundles  of  olfactory  nerve-fibres ;  e,  the  alveoli   of  serous 
(Bowman's)  glands.    (Atlas.) 

of  the  respiratory  part  of  the  nasal  cavity  ;  in  most 
places,  however,  the  cilia  are  absent ;  the  former 
condition  obtains  in  those  places  which  are  in  close 
proximity  to  the  respiratory  region. 

(b)  Between  the   epithelial  cells  extend  spindle- 
shaped   cells,  each  with  a  spherical,  or  very  slightly 


336  Elements  of  Histology.      [Chap.  xlii. 

oval,  nucleus — the  sensory  cells  (Max  Schultze). 
Each  cell  sends  one  broad  process  towards  the  free 
surface,  over  which  it  projects  in  the  shape  of  a  small 
bundle  of  shorter  or  longer  rods ;  whereas  a  fine 
varicose  filament  passes  from  the  cell  body  towards 
the  mucosa,  and,  as  shown  first  by  M.  Schultze,  be- 
comes connected  with  a  fibrilla  of  the  network  of  the 
olfactory  nerve-fibres. 

(c)  In  some  places  there  is  a  deep  layer  of  epithe- 
lial cells,  each  with  a  spherical  nucleus,  of  an  inverted 
cone  in  shape,  their  pointed  extremity  passing  be 
tween  the  other  cells  just  mentioned  and  their  broad 
basis  resting  on  the  basement  membrane.  Yon 
Brunn  has  shown  that  there  is  on  the  free  surface  of 
the  epithelium  a  sort  of  cuticle — a  delicate  limitans 
externa. 

491.  The  mucous  membrane  is  of  loose  texture, 
and  contains  a  rich  plexus  of  bundles  of  olfactory 
nerve-fibres,  extending  chiefly  in  a  direction  parallel 
to  the  surface.  Each  olfactory  nerve-fibre  is  non- 
raedullated,  i.e.,  is  an  axis  cylinder  composed  of  minute 
or  primitive  fibrillar,  and  invested  in  a  neurilemma  with 
the  nuclei  of  the  nerve  corpuscles.  Near  the  surface 
the  fibres  of  the  plexus  are  thin,  and  they  split  up 
into  the  constituent  fibrils  which  form  a  network  ;  into 
this  pass  the  fine  varicose  processes  of  the  sensory 
cells  above  named. 

492.  The  blood-vessels  supply  with  capillary  net- 
works the  superficial  part  of  the  mucous  membrane 
and  the  numerous  glands.  These  are  the  glands  of 
Bowman,  extending  through  the  thickness  of  the 
mucous  membrane.  They  are  tubes,  slightly  branched, 
and  gradually  enlarging  towards  their  distal  end ;  in 
some  parts  they  are  more  or  less  straight.  In  struc- 
ture they  are  identical  with  serous  glands,  possessing 
a  minute  lumen,  and  being  lined  with  a  layer  of 
columnar  albuminous  cells.     The  duct  is  a  very  fine 


chap,  xlii.]   Nasal  Mucous  Membrane.  337 

canal ;  it  is  that  part  of  the  gland  that  is  situated 
in  the  epithelium  of  the  free  surface ;  it  passes  verti- 
cally through  this,  and  consists  of  a  fine  limiting 
membrane,  the  continuation  of  the  membrana  propria 
of  the  gland-tube,  and  a  layer  of  very  flattened  epi- 
thelial cells. 

493.  There  is  a  definite  relation  between  the 
size  and  number  of  the  bundles  of  the  olfactory  nerve- 
fibres,  the  thickness  of  the  olfactory  epithelium,  and 
the  length  of  the  gland-tubes.  The  size  and  number 
of  the  bundles  of  the  nerve-fibres  are  determined 
by  the  thickness  of  the  epithelium — i.e.,  by  the 
number  of  the  sensory  cells  ;  the  number  and  thick- 
ness of  the  olfactory  nerve  bundles  determine  the 
thickness  of  the  mucous  membrane,  and  the  thicker 
it  is,  the  longer  are  the  glands  of  Bowman. 

494.  The  organ  of  Jacob §011  is  a  minute 
tubular  organ  present  in  all  mammals,  and,  as  has 
been  shown  by  Dursy  and  Kolliker,  also  in  man.  In 
mammals  it  is  a  bilateral  tube,  compressed  from  side 
to  side,  and  situated  in  the  anterior  lower  part  of 
the  nasal  septum.  Each  tube  is  supported  by  a 
hyaline  cartilage,  in  the  shape  of  a  more  or  less 
plough-shaped  capsule — the  cartilage  of  Jacobson 
— and  opens  in  front  directly  into  the  nasal  furrow 
(guinea-pig,  rabbit,  rat,  &c.) ;  or  it  leads  into  the  canal 
of  Stenson  (dog),  which  passes  through  the  canalis 
naso-palatinus,  and  opens  immediately  behind  the 
incisor  teeth  on  the  palate.  In  all  instances,  how- 
ever, it  terminates  posteriorly  with  a  blind  ex- 
tremity. 

49.5.  The  cavity  of  the  tube  is  lined  with  stratified 
columnar  epithelium,  which  on  the  lateral  wall  is 
ciliated  in  the  guinea-pig  and  dog,  and  non-ciliated  in 
the  rabbit.  The  median  wall — i.e.,  the  one  next  to 
the  middle  line — is  lined  with  olfactory  epithelium, 
identical  with  that  of  the  olfactory  region  of  the  nasal 
w 


338  Elements  of  Histology.    [Chap,  xliii. 

cavity.  Branches  of  olfactory  nerve-fibres  also  pass 
into  the  median  wall,  and  behave  in  exactly  the  same 
manner  as  in  the  olfactory  region.  Numerous  serous 
glands — belonging  chiefly  to  the  upper  and  lower 
wall — open  into  the  cavity  of  the  organ  of  Jacobson. 

In  the  lateral  wall  there  is  in  many  instances  a 
plexus  of  veins,  extending  in  a  longitudinal  direction, 
and  between  the  vessels  are  bundles  of  non-striped 
muscular  tissue,  thus  constituting  a  sort  of  cavernous 
tissue. 


CHAPTER    XLIII. 

THE      DUCTLESS      GLANDS. 

496.  I.  The  hypophysis  cerebri. — The  upper 
or  smaller  lobe  belongs  to  the  central  nervous  system. 
The  lower  or  larger  lobe  is  surrounded  by  a  fibrous 
capsule,  which  sends  numerous  minute  septa  into  the 
interior.  These  split  up  into  numerous  trabecule  of 
fibrous  tissue,  which,  by  dividing  and  re-uniting,  form 
a  dense  plexus,  with  smaller  and  larger,  spherical  or  ob- 
long, or  even  cylindrical  spaces — the  alveoli.  In  these 
lie  spherical  or  oblong  masses  of  epithelial  cells.  These 
epithelial  cells  are  columnar,  pyramidal,  or  polyhedral, 
each  with  an  oval  or  spherical  nucleus.  Between  the 
epithelial  cells  of  the  same  group  are  found  here  and 
there  small  branched  or  spindle-shaped  cells,  with  a 
small  flattened  nucleus.  In  some  of  the  groups  or 
alveoli  of  epithelial  cells  is  a  cavity,  a  sort  of  lumen, 
filled  with  a  homogeneous  gelatinous  substance. 

The  interalveolar  connective  tissue  contains  a 
network  of  capillaries.  Between  the  alveoli  and  the 
interalveolar  tissue  there  are  lymph  sinuses,  like  those 
around  the  alveoli  of  other  glands — e.g.,  the  salivary 
glands. 


chap,  xliii.]      The  Ductless  Glands. 


339 


497.  II.  The  thyroid  gland  (Fig.  167).— The 
framework  of  this  gland  is  in  many  respects  similar 
to  that  of  other  glands,  there  being  an  outer  fibrous 
capsule,  thicker  and  thinner  septa,  and  finally  the  fine 
trabecule  forming  the  septa  between  the  gland  alveoli. 
These  are  closed  vesicles  of  a  spherical  or  oval  shape, 
and  of  various  sizes.  Each  vesicle  is  lined  with  a  single 
layer  of  polyhedral  or 
columnar  epithelial  cells, 
each  with  a  spherical  or 
oval  nucleus.  There  is  a 
cavity,  which  differs  in  size 
according  to  the  size  of  the 
vesicle.  It  contains,  and 
is  more  or  less  filled  with, 
a  homogeneous,  viscid,  albu- 
minous fluid — the  so-called 
colloid.  In  this  often  oc- 
cur degenerating  nucleated 
lymph  -  corpuscles  and 
coloured  blood  -  corpuscles 
(Baber). 

498.  The  vesicles  are 
surrounded  by  networks  of 
blood    capillaries.       In    the 

connective  tissue  framework  lie  networks  of  lym- 
phatics ;  between  the  framework  and  the  surface  of  the 
vesicles  are  lymph  sinuses  lined  with  endothelium 
(Baber).  The  large  and  small  lymphatics  are  often 
filled  with  the  same  colloid  material  as  the  vesicles, 
and  it  is  probable  that  this  colloid  material  is  produced 
in  the  vesicles,  and  carried  away  by  the  lymphatics, 
to  be  finally  discharged  into  the  circulating  blood. 

499.  Its  formation  in  the  vesicles  is  probably  due 
to  an  active  secretion  by  the  epithelial  cells  of  the 
vesicles,  and  to  a  mixture  with  it,  or  maceration  by 
it;  of  the  effused  blood  mentioned  above.      In  some 


Fig.  167.  —  From  a  Section 
through  the  Thyroid  Gland 
of  Dog. 

p,  The  epithelium  lining  the  vesi- 
cles ;  b,  the  "  colloid"  contents  of 
the  vesicles ;  c,  a  lymphatic  filled 
with  the  same  material  as  the 
vesicles ;  d,  the  flhrous  tissue  be- 
tween the  gland  vesicles. 


34° 


Elements  of  Histology.     [Chap,  xliii. 


instances  Baber  found  the  amount  of  blood  effused 

into  the  cavity  of 
the  vesicles  very 
considerable,  and 
hence  it  is  justifi- 
able to  assume  that 
the  destruction  of 
red  blood-corpus- 
cles forms  one  of 
the  functions  of  the 
thyroid  gland. 

500.  III.  The 
suprarenal 
bodies  (Fig.  168). 
— The  suprarenal 
body  is  enveloped 
in  a  fibrous  cap- 
sule ;  in  connection 
with  this  are  septa 
and  trabeculse  pass- 
ing inwards,  and 
they  are  arranged 
differently  in  the 
cortex  and  in  the 
medulla  of  the 
gland,  as  will  be 
seen  presently. 

The  cortex  of 
the  gland  consists 
of  an  outer,  mid- 
dle, and  inner 
zone,  all  three  be- 
ing directly  con- 
tinuous with  one 
another.  The  outer 
one  is  the  zona 
numerous    spherical,    or, 


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Pig.  168.— From  a  Vertical  Section  through 
the  Suprarenal  Body  of  Man. 

1,  Cortical  substance  :  2,  medullary  part ;  a,  outer 
capsule;  6,  zona  plomerulosa;  o,  zona  fascicu- 
lata;  d,  zona  reticularis ;  e,  medulla ;  /,  a  large 
vein.    (Elberth,  in  Strieker's  Manual.) 


(jlomeruloaa ;     it     contains 


Chap,  xliii.]      The  Ductless  Glands.  341 

more  commonly,  elongated,  masses  of  epithelial  cells. 
The  cells  are  polyhedral  or  cylindrical,  each  with  a 
spherical  or  oval  nucleus.  In  some  animals — as  the 
dog,  horse — the  cells  are  thin  and  columnar,  and 
arranged  in  a  transverse  manner.  Occasionally  a  sort 
of  lumen  can  be  discerned  in  some  of  these  cell  masses. 

501.  Next  follows  the  middle  zone,  or  zona 
fasciculata.  This  is  the  most  conspicuous  and 
broadest  part  of  the  whole  gland.  It  consists  of 
vertical  columns  of  polygonal  epithelial  cells,  each 
with  a  spherical  nucleus.  The  cell  substance  is  trans- 
parent, and  often  contains  an  oil  globule.  The  columns 
anastomose  with  their  neighbours.  Between  the 
columns  are  fine  septa  of  connective  tissue  carrying 
blood  capillaries. 

Between  the  cell  columns  and  the  connective  septa 
are  seen  here  and  there  lymph  spaces,  into  which  lead 
fine  channels,  grooved  out  between  some  of  the  cells  of 
the  columns. 

502.  Next  follows  the  inner  zona,  or  zona  reticu- 
laris, composed  of  smaller  or  larger  groups  of  poly- 
hedral cells,  with  more  or  less  rounded  edges.  These 
cell-groups  anastomose  with  one  another.  The  indi- 
vidual cells  are  slightly  larger,  and  their  substance  is 
less  transparent  than  those  of  the  zona  fasciculata.  In 
the  human  subject  they  are  slightly  pigmented. 

503.  In  the  medulla  we  find  cylindrical  streaks 
of  very  transparent  cells  ;  the  streaks  are  separated  by 
vascular  connective  tissue.  The  cells  are  polyhedral, 
columnar,  or  branched.  These  cell-streaks  anasto- 
mose with  one  another,  and  are  directly  continuous 
with  the  cell-groups  of  the  zona  reticularis  of  the 
cortex. 

504.  The  cortex  is  richly  supplied  with  dense 
networks  of  capillary  blood-vessels ;  their  meshes  are 
polyhedral  in  the  outer  and  inner  zone,  elongated  in 
the  middle  zone,  or  zona  fasciculata.     In  the  medulla 


342  Elements  of  Histology.     [Chap,  xliii. 

numerous  plexuses  of  veins  are  met  with.  In  the 
centre  of  the  suprarenal  body  lie  the  large  efferent 
venous  trunks.  In  the  capsule  (Kolliker,  Arnold), 
and  in  the  connective  tissue  around  the  central  veins, 
are  plexuses  of  lymphatic  tubes  with  valves.  The 
nerves  are  very  numerous,  and  composed  of  non- 
medullated  fibres ;  in  the  medulla  they  form  rich 
plexuses.  In  connection  with  these  and  with  those  of 
the  outer  capsule  are  small  ganglia  (Holm,  Eberth). 

505.  IV.  The  glandula  coccygea  and  in- 
tercarotica. — The  first  of  these  is  a  minute  corpuscle 
situated  in  front  of  the  apex  of  the  os  coccygis,  and 
was  discovered  by  Luschka.  The  glandula  carotica 
of  Luschka  (ganglion  intercaroticum)  is  of  exactly  the 
same  structure  as  the  glandula  coccygea. 

506.  Its  framework  is  of  about  the  same  nature  as 
that  of  other  glands — a  fibrous  capsule  and  inner 
fibrous  septa  and  trabecular  The  septa  and  trabecule 
contain  in  some  places  bundles  of  non-striped  muscular 
tissue  (Sertoli). 

507.  The  spaces  of  the  framework  are  occupied  by 
the  parenchyma.  This  consists  of  spherical  or  cylin- 
drical masses  of  cells  connected  into  networks.  The 
individual  cells  are  polyhedral  epithelial  cells,  each 
with  a  spherical  nucleus.  According  to  Luschka,  in 
the  new-born  child  they  are  ciliated.  In  the  centre 
of  each  of  the  cell-masses  lies  a  capillary  blood-vessel, 
much  convoluted  and  wavy. 

Numerous  non-medullated  nerve-fibres  forming  a 
plexus  are  situated  in  the  framework  of  the  gland. 


INDEX. 


Absorption  (see  Lymphatics) . 

Achromatin,  9. 

Acini  of  glands,  180,  182. 

of  liver,  211. 

of  pancreas,  209. 

Adenoid  reticulum,  44,  80,  92. 

tissue,  92. 

Adrnaxillary  glands,  179. 
Adventitia  of  arteries,  76,  78. 

of  capillaries,  80,  93. 

of  veins,  79. 

lymphatic  vessels,  102. 

Agininated  glands,  95. 
Air  cells,  220. 
A  Ise  nasi,  46. 
Albuginea  of  ovary,  258. 
Albumin  membrane  of  Ascherson, 

273. 
Albuminous  cells,  183. 
Alveolar  cavity,  171,  178. 

ducts,  65,  220. 

Alveoli  of  glands,  180, 182. 

of  lung,  220. 

of  pancreas,  209. 

Amoeboid  corpuscles,  9. 

movement,  4,  5,  14,  41,  90,  93. 

Ampulla,  320,  323. 
Auterior  commissure,  157. 

nerve-roots  from  cord,  136. 

Aorta,  65,  78. 
Aponeurosis,  32. 
Aqueductus  cochleae,  321 

Sylvii,  150,  160. 

vestibuli,  321. 

Arachnoid   membrane    of    spinal 

cord,  127. 

of  brain,  149. 

Arachnoidal  villi,  149. 
Areolar  tissue,  33. 
Arrector  pili,  64,  287. 
Arteriae  ciliares  breves,  305. 

recurrentes,  305. 

helicinae,  256. 

rectae,  242. 

Arteries,  65,  76. 
Arterioles,  Afferent,  40,  51. 


Arterioles  of  ovary,  267. 
Articular  cartilage,  47,  60. 
Articulation  nerve-corpuscles,121. 
Arytenoid  cartilage,  215. 
Ascending  loop-tube,  238. 
A  ster  stage  in  nucleus,  8. 
Auditory  hairs,  324. 

nerve,  Origin  of,  149. 

,  Division  of,  148. 

teeth,  328. 

Auerbach's  plexus,  170,  201,  207. 
Auricle  of  heart,  75. 
Auriculo-ventricular  valves,  75. 
Axis  cylinder,  107. 

process  of  sympathetic 

ganglion  cell,  169. 

Bartholin's  glands,  270. 
Basement  membranes  of  skin,  277. 
Basilar  membrane  of  cochlea,  327, 

328. 
Bellini's  ducts,  239. 
Bile-duct,  213,  214. 
Bile  capillaries,  213. 
Bilirubin,  13. 
Bladder,  64,  243. 
Blastoderm  of  chick,  2. 
Blood,  10. 

corpuscles,  10,  13. 

,  their  origin,  15. 

glands  of  His,  92. 

-plates  of  Bizzozero,  15. 

vessels  in  grey  matter,  151. 

Bone,  50. 

■,  Development  of,  55. 

cartilage,  50. 

cells,  31,  53. 

trabeculae,  54. 

corpuscles,  53. 

Bowman's  capsule,  234. 

elastica  anterior,  44. 

glands,  336. 

membrane,  295. 

sarcous  elements,  68. 

birain  membranes,  149. 
Brainsand,  163. 


344 


Elements  of  Histology. 


Bronchi,  65,  219. 

Brownian   molecular   movement, 

189 
Brucn,  Glands  of,  294. 
Briicke's  elementary  organisms,  5. 

oikoid  and  zooid,  12. 

tunica  nervea,  317. 

Brunner's  glands,  208,  209. 
Buccal  glands,  187. 
Bulbus  olfactorius,  159. 
Biitschli  s  nuclear  spindle,  9. 

Calcification  of  bone,  55. 

of  cartilage,  47. 

of  dentine,  62'. 

Calices  of  kidney,  230. 
Canal  of  Schlemm,  299. 

of  Stenson,  337. 

of  Stiffing,  307. 

Canalis  liyaloideus,  307. 

Petiti,  307. 

reuniens,  322. 

Canaliculi  in  bone,  52. 

in  cartilage,  48. 

Capillaries  of  marrow-bone,  81. 

of  nerve  system,  80. 

Capillary  bile-ducts,  213. 

blood-vessels,  80,  201. 

lymphatics,  86. 

network  in  mucosa,  190. 

sheaths,  228. 

Capsule,  External,  of  brain,  162. 

,  Internal,  of  brain,  162,  163. 

of  Glisson,  210. 

of  kidney,  65. 

of  the  spleen,  65,  225. 

Cartilage,  45. 

,  Articular,  47,  60. 

cells,  31,  48. 

,  Elastic,  49. 

,  Fibrous,  48. 

,  Hyaline,  46. 

,  Lacunse,  46. 

of  Jacobson,  337. 

of  Luscbka,  215. 

Cavernous      tissues      in     genital 

organs,  255. 
Cavities  of  tendon  sheatbs,  88. 
Cavum  tympani,  319. 
Cells,  5. 
,  Muscular,  of  blood-vessels, 

65. 

,  of  intestine,  65. 

,  of  respiratory  organs,  65. 

,  of  stomach,  65. 

,  of  urinary  organs,  65. 

in  tadpole's  tail,  35. 

of  Claudius,  327,  331. 

Cellulee  mastoidese,  319. 


Cellular  tissue,  33. 
Cement  of  teetb,  174. 

substance,  80,  82,  90. 

of  endothelium,  25. 

of  epithelium,  17. 

of  fibrous  tissue,  32. 

Central  canal,  128. 

grey  nucleus,  134. 

Centroacinous  cells,  210. 
Centrum  ovale,  156, 157. 
Cerebellum,  149, 152. 
Cerebrum,  149,  156,  157. 
Ceruminous  glands,  278,  318. 
Cervix  of  uterus,  266. 
Cbalice  cells,  22. 
Chondrin,  31,  45. 
Chondroclasts,  62. 
Choroidal     portion     of      ciliary 

muscle,  64. 
Choroid  membrane,  303. 
Chromatin,  9. 
Chyle,  206. 
Ciliary  muscle,  65,  300. 

nerve,  163. 

processes,  303. 

Ciliated  cells,  21. 
Circulus  arteriosus  in  iris,  302. 
Circumanal  glands,  278. 
Cisterna  lympbatica  magna,  89. 
Clarke's  columns,  137,  140. 
Claustrum,  159,  162. 
Cleavage  of  ovum,  2. 

of  wbite  blood  corpuscles,  15. 

Clitoris,  270. 

Cochlea,  320,  324. 

Cohnheim's  areas,  70. 

Colloid,  339. 

Colostrum  corpuscles,  273. 

Coloured  blood  corpuscles,  10. 

Colourless  blood  corpuscles,  13. 

Columnar  epithelial  cells,  17. 

Commissure,  Grey,  of  spinal  cord, 

128. 

,  "White,  of  spinal  cord,  135. 

Compound  lymphatic  glands,  98. 

Conarium,  163. 

Concentric  bodies  of  Hassall,  97. 

lamellse,  53. 

Cone  fibre,  316. 
Cones  of  retina,  313. 
Coni  vasculosi,  250. 
Conjunctiva,  291. 

blood-vessels,  293. 

bulbi,  293. 

lymphatics,  293. 

nerves,  294. 

palpebree,  291,  293. 

Connective  tissue,  31. 
Contraction  wave,  67. 


Index. 


345 


Contractility     of     corneal     cor- 
puscles, 37. 

— —  of  pigment  cells,  28. 

Convolution  in  brain,  157. 

in  nucleus,  8. 

Cordse  tendineae,  75. 

Cords  of  adenoid  tissue,  94. 

Corium,  274. 

Cornea,  20,  295. 

nerves  in,  297. 

Corneal  cells,  36. 

corpuscles,  34,  297. 

Cornu  Ammonis,  158,  159. 

Cornua  uteri,  267. 

Corona  radiata,  163. 

Corpora  albicantia,  161,  163. 

cavernosa,  65,  2^5. 

quadrigemina,  16). 

striata,  161, 162. 

Corpus  callosum,  157. 

Highmori,  244. 

luteum,  262. 

restiforme,  144,  142. 

spongiosum,  255. 

Corpuscles,  Malphigiau,  227,  233. 

of  blood,  10,  13. 

of  bone,  53. 

of  connective  tissue,  36. 

of  Grandry,  120. 

of  Herbst,  115,  118. 

of  Ivmpb,  90,  93. 

of  Meissner,  115,  118. 

of  muscle,  70. 

of  nerve,  108 

of  Pacini,  115,  121,  291. 

of  Vater,  115. 

,  Tactile,  115,  118. 

C'orti's  arcb,  330. 

cells,  351. 

ganglion,  326. 

rods,  329. 

Cortical  layer  of  ovary,  258. 

lymph-sinus,  101. 

Costal  cartilages,  46. 

pleura,  89. 

Cowper's  glands,  254,  270. 

Cremaster  internus,  252. 

Crescents  of  Gianuzzi,  183. 

Cricoid  cartilage,  46. 

Crista  acustica,  323. 

spiralis,  327,  332. 

Crus  cerebri,  142,  161. 

,  Crusta  of,  163. 

Crusta  petrosa,  171. 

Crypts,  95. 

of  Lieberkuhn,  203,  20^. 

Cuticle  of  Nasmyth,  172,  177. 
Cutis  anserina,  287. 

vera,  274. 


Cystic  duct,  65. 
Cytogenous  tissue,  92. 

Deiters'  cells,  150,  331. 

phalanges,  332. 

processes,  141,  145. 

Demilunes  of  Heidenhain,  183. 
Dentinal  canals,  173. 

fibres,  62,  173. 

sheaths,  173. 

tubes,  62. 

Dentine,  62,  172,  173. 
Descemet's  membrane,  44. 
Diapedesis,  82. 
Diaphragm,  73,  88. 
Diaster  stage  in  nucleus,  8. 
Diffuse  adenoid  tissue,  93. 
Dilatator,  65. 

pupillse,  302. 

Direct  division,  7,  9. 

"  Disc  tactil,"  121. 

Discus  proligerus,  261. 

Disdiaclasts,  74. 

Distal  convoluted  tubes,  238. 

Division,  Bemak's  mode  of,  7. 

Doyere's  nerve-mount,  125. 

Ductless  glands,  338. 

Ducts  of  pancreatic  gland,  65. 

of  salivary  gland,  65. 

D actus  ejaculatorii,  253. 
Dura  mater,  127. 
Dural  sheath,  317. 

Ear,  External,  318. 

,  Internal,  320. 

Efferent  lymphatics,  102. 

medullated  nerve-fibres,  116. 

veins,  40. 

Elastic  fenestrated  membrane  of 

Henle,  44. 
Elastin,  43. 
Electric  nerve,  111. 
Eleidin,  20. 
Elementary  fibrillse,  107. 

fibrils,  32. 

organisms,  4. 

Enamel,  171. 

cap, 175. 

cells,  175,  177. 

organ,  175,  177. 

prisms,  171. 

End-bulbs    of    Erause,  115,    119, 

294. 
Endocardium,  74,  76. 
Endochondral  formation  of  bone, 

55. 
Endolymph,  321. 
Endomysium,  66. 


346 


Elements  of  Histology. 


Endoneurium,  105. 
Endothelial  cells,  structure,  25. 

membrane,  25. 

Endothelium,  25. 
Endotheloid  cell-plates,  92. 
Engelmann's  lateral  disc,  68. 
E  pi  cerebral  space,  150. 
Epidermis,  19,  274. 
Epididymis,  65,  250. 
Epiglottis,  49,  93. 
Epineurium,  104. 
Epithelial  cells,  16. 

division  of,  24. 

regeneration  of,  24. 

Epithelium,  19. 
Epitheloid  layer,  56. 
Eustachian  tube,  319. 
External  arcuate  fibres,  144,  147. 

capsule  of  brain,  162. 

Eye,  290. 

lashes,  292. 

lids,  291. 

Fasciae,  87. 
Fascicles,  66. 
Fasciculus  cuneatus,  144. 

gracilis,  144. 

of  Goll,  132, 144. 

of  Turk,  132,  142,  145. 

pyramidal  direct,  132. 

Fat  cells,  39. 

and  starvation,  41. 

Femur,  60. 
Fenestra  ovalis,  320. 

rotunda,  320. 

Fenestrated   membrane,    30,    33, 
127. 

of  Henle,  77. 

Fertilisation  of  ovum,  2. 

Fibree  arcuatse,  296. 

Fibres,  Connective  tissue,  31. 

,  Elastic  tissue,  50. 

of  muscle,  63,  66,  72. 

of  nerves,  103. 

of  Purkinje,  75. 

Fibrillse  of  connective  tissue,  32. 

of  muscle,  64. 

of  nerve,  107. 

Fibro-cartilage,  48. 

Fibrous  tissue  development,  42. 

Fillet,  160. 

Fissura  orbitalis,  65. 

Fissures  of  spinal  cord,  130. 

Foetal  tooth  papilla,  176. 

Follicles,  Lieberktihn's,  203. 

,  Lymph,  92,  94,  100. 

,  Sebaceous,  286. 

,  Thymus,  96. 

Fornix  conjunctiva?,  293. 


Fornix  vaginal,  269. 
Fossa  glenoidalis,  48. 

navicularis,  254. 

patillaris,  307. 

Sylvii,  159. 

Fovea  centralis,  310,  314,  315 

hemieiliptica,  320. 

hemispherica,  320. 

Fundus,  266. 

Funiculus  of  Rolando,  144. 

Gall-bladder,  65. 

Ganglia,  Cerebro-spinal,  138,  141. 

,  Sympathetic,  168. 

Ganglion  cells,  138, 164. 
Gasserian  ganglion,  163. 
Gelatinous  tissue,  45. 
Geniculate  ganglion,  163. 
Genital  corpuscles  of  Krause,  120. 

end-corpuscles,  115. 

organs  (male),  244. 

(female),  257. 

Germ  reticulum  of  von  Ebner,  247. 
Germinal  endothelial  cells,  28. 

epithelium,  258. 

spots,  1,  259. 

vesicle,  1,  259. 

Germinating  cells,  29. 
Giralde"'s  organ,  251. 
Gland,  Prostate,  253. 
Glands,  Bartholini,  270. 

,  Brunner,  208,  209. 

,  Buccal,  187. 

,  Carotic,  342. 

,  Ceruminous,  278,  318. 

,  Coccygeal,  342. 

,  Harder,  295. 

,  Krause,  293. 

,  Lachrymal,  294. 

,  Lieberktihn's,  17. 

,  LittrtS,  254. 

,  Lymphatic,  80,  84, 100. 

,  Meibomian,  292. 

,  Mohl,  292. 

,  Mucous,  179,  191. 

,  Peptic,  197. 

,  Peyer,  95,  205. 

,  Pyloric,  199. 

,  Salivary,  178. 

,  Sebaceous,  287. 

,  Solitary,  95. 

,  Submaxillary,  179. 

,  Sweat,  276. 

Glandulae  agminatse,  200. 

lenticulares,  200. 

Pacchioni,  149. 

uterinse,  266. 

ftlans  clitoridis,  270. 
penis,  255. 


Index. 


347 


Glassy  membrane,  231. 
Glisson's  capsule,  210. 
Globulin,  12. 
Glomerule,  159. 
Glutin,  31,  33. 
Glycogen,  14. 
Goblet  cells,  18,  22. 
Graafian  follicles,  258,  263. 
Granary's  corpuscles,  120. 
Granular  formation  of  Meynert, 
159. 

layer  of  Purkinje,  174. 

Granules  in  blood,  15. 
Granulosa  membrana,  259. 
Grey  commissure,  128. 
Ground  lamellae,  53. 

plexus  of  Arnold,  121. 

substance,  117. 

Growing  capillaries,  82. 

Habenula  perforata,  331. 
Hsamatin,  13. 
Hsematoidin,  13. 
Heematoplasts,  15. 
Hsemin  crystals,  13. 
Haemoglobin,  12. 

crystals,  13. 

Hair,  278. 

bulb,  282,  285. 

,  Development  of,  285. 

—  fibres,  282. 

—  follicles,  278,  280. 
knob,  285. 

,  Marrow  of,  282. 

,  New  formation  of,  284. 

papilla,  285. 

,  Eoot  of,  282. 

sheath  of,  281. 

sac,  280. 

,  Shaft  of,  279,  283. 

Harder*  s  gland,  295. 
Haversian  canals,  53. 

lamellse,  53. 

spaces,  54. 

Heart  and  blood-vessels,  74. 
HeUcotrema,  320. 
Hemisphere  of  brain,  152. 
Henle,    Fenestrated    membranes 
of,  44,  77. 

,  Fibres  of,  44. 

,  Sheath  of,  105. 

,  Stratum  nerveum  of,  317. 

,  Tubes  of.  237 

Hensen's  cells,  331. 
Hepatic  cells,  212. 

duct,  65. 

lobules,  211. 

veins,  211. 

Herbst,  Corpuscles  of,  115, 118. 


Hilum  of  glands,  98. 

of  salivary  glands,  180. 

of  spleen,  226. 

Hippocampus,  159. 
Homogeneous  elastic  membranes, 

44. 
Howship's  lacunae,  62. 
Hyaline  cartilage,  46. 
Hyaloid  membrane,  307. 
Hypophysis,  161,  338. 

Ileum,  205. 

Incremental  lines  of  Salter,  174. 

Incus,  320.      ' 

Indirect  division,  7. 

Infundibula,  65,  161,  163. 

of  bronchiole,  220. 

of  gland,  188. 

Inner  molecular  layer,  311. 

nuclear  layer,  311. 

Interarticular  cartilages,  48. 
Interfascicular  spaces,  34,  36. 
Interglobular  spaces  of  Czermak, 

174. 
Interlobar  ducts,  180. 
Interlobular  bile-ducts,  213,  214. 
connective   tissue  of    liver, 

210. 

ducts,  180. 

Intermediary  cartilage,  48. 

plexus,  121. 

zone,  200. 

Intermembranous    formation    of 

bone,  55,  61. 
Intermuscular  fibrils,  122. 
Internal  capsule  of  brain,  163. 
Interstitial  lamellae,  53. 
Intervertebral  discs,  48. 
Intestine,  Large,  201 

,  Small,  201. 

Intima  of  arteries,  76,  77. 
Intralobular  bile-vessels,  213. 

ducts,  180. 

Intranuclear  network, 
Iris,  300. 

,  Blood-vessels  of,  302. 

,  Lympn-clefts  of,  302. 

,  Lymph-sinuses  of,  302. 

,  Nerve-fibres  of,  302. 

Island  of  Eeil,  162. 

Jacobson's  organ,  337,  338. 

Karyokinesis,  7,  43,  247. 
Kidney,  229. 

,  Afferent  arterioles  of,  240. 

blood-vessels,  240. 

glomerulus,  234. 


348 


Elements  of  Histology. 


Kidney  lymphatics,  214,  215,  243. 

parenchyma,  231. 

vessels,  241. 

Kdlliker's  osteoclasts,  62. 

Labia  pudendi  majora,  287. 
Labium  tympanicum,  327. 

vestibulare,  327. 

Labyrinth,  Osseous,  320. 
Lachrymal  glands,  294. 
Lacunae  Morgagni,  254. 

of  bone,  52,  53. 

of  cartilage,  46. 

of  lymphatics,  86. 

Lamellae  of  bone,  54. 

of  cornea,  296. 

of  lens,  306. 

Lamina  cribosa,  317. 

elastica  of  cornea,  295. 

fusca,  299. 

■ reticularis,  332. 

spiralis  ossea,  320. 

■ vitrea,  301,  305. 

Langerhans'  granular  layer,  20. 

Larynx,  215. 

Lateral  basilar  process,  158. 

nucleus,  145. 

tract,  143. 

Lens,  305. 

fibres,  306. 

stars,  306. 

Lenticular  glands,  95. 
Ligamentum  denticulatum,  128. 

latum,  65. 

pectinatum,  299. 

pulmonis,  221. 

spirale  accessorium,  326,  328. 

suspensory  of  lens,  307. 

Limitans  externa,  312. 

interna,  310. 

Lines  of  Schreger,  174. 
Liquor  folliculi,  260. 

sanguinis,  10. 

Littre"'s  glands,  254. 
Liver,  88,  210. 

vessels  of,  211,  212. 

Lobes  of  pancreas,  203. 

of  salivary  gland,  180. 

of  thymus  gland,  96. 

—  of  lung,  220. 
Lobules  of  liver,  211. 

of  lung,  220. 

of  salivary  glands,  180. 

of  thymus  gland,  96. 

Lung,  88,  219. 

blood-vessels,  223. 

lymphatics,  223. 

Lymph,  90. 

Lymphatic  capillaries,  86. 


Lymphatic  clefts,  79,  86. 

glands,  80, 84,  100. 

rootlets,  86. 

sinuses,  88,  101. 

tissue,  85. 

vessels,  79,  84,  92. 

Lymphatics,  65,  201. 

in  mucosa,  190. 

Lymph-canal  system  in  cornea,  36. 

canalicular  system,86, 90, 297. 

cavities,  88. 

corpuscles,  90,  93. 

f  ollicles,  92,  94. 

hearts,  90. 

Lymphoid  cells,  29. 

Macula  acustica,  323. 

lutea,  310, 311,  314,  315. 

Malleus,  320. 

Malpighian  corpuscles  of  kidney, 

233. 

of  spleen,  227. 

■ pyramids  of  kidney,  231. 

stratum  of  skin,  19. 

Mammary  gland,  270. 
Manubrium  mallei,  318. 
Marrow  of  bone,  50. 
Matrix  of  osseous  substance,  52. 
Meatus  auditorius  externus,  318. 
Meckel's  ganglion,  163. 
Media  of  arteries,  76. 
Median  lateral  fissure,  132. 
Mediastinum  testis,  244. 
Medulla  oblongata,  142. 
- —  of  gland,  99. 
Medullary  cylinders,  100. 

lymph-sinus,  101. 

ray,  231. 

sheath  of  nerve-fibres,    107, 

103. 
Medullated  nerve-fibres,  106,  114, 

137. 
Meibomian  glands,  292. 
Meissner's  corpuscles,  191,  291. 

plexus,  170,  201,  207. 

Membrana  basilaris,  327,  328. 

chorio-capillaris,  304. 

Descemeti,  297. 

granulosa,  259. 

hyaloidea,  307. 

secundaria,  322. 

supra-choroidea,  303. 

tectoria,  332. 

tympani,  318. 

Membranes  of  Krause,  67,  74. 
Mesencephalon,  159. 
Mesentery,  88. 
Mesogastrium,  30. 
Migratory  cells,  41. 


Index'. 


349 


Milk,  273. 

globules,  272. 

tooth, 177. 

Modiolus,  320,  326. 
Motor  ganglion  cells,  141. 
Movement  of  cilia,  22. 
Mucin,  23. 
Mucosa,  189. 

,  Lymph  follicles  of,  200. 

Mucous  cells,  183. 

glands,  179,  191. 

membrane,  189. 

Muco-salivary  glands,  179. 
Mucus,  formation  of,  23. 
MuUer's  fibres,  310. 

muscle,  300. 

Muscle  bundles,  64. 

cells,  64. 

corpuscles,  70. 

fibres,  63,  72. 

tissue,  striped,  66,  189. 

,  Non-striped,  68,  65. 

Muscular  compartments,  67. 
Muscularis  externa,  196. 

mucosae,  64, 195. 

Musculus  ciliaris  Eiolani,  292. 

Myeloplax,  6. 

Myeloplaxes  of  Eobin,  51,  62. 

Nail,  288. 

cells,  289. 

groove,  288. 

substance,  289. 

Nasal  mucous  membrane,  333. 

septum,  46. 

Nerve  bundles,  104. 

corpuscles,  108. 

end  plate,  124. 

endings,  112,  115. 

fibres,  103. 

plexus,  106,  111,  114. 

Network  of  fibrillse,  111. 
Neurilemma,  108. 
Neuroglia,  133. 

cells,  133. 

fibrils,  133, 150. 

of  Virchow,  45. 

tissue,  130. 

Neurokeratin,  107,  109,  135,  313. 

Nipple,  65. 

Non-medullated  nerve-fibres,  111, 

114. 
Norris's  blood  corpuscles,  13. 
Nuclear  layer   in    bulbus    olfac- 

torius,  159. 

zone,  306. 

Nuclein,  6. 
Nucleoli,  6. 
Nucleus,  Structure  of,  6. 


Nucleus  caudatus,  162. 

cuneatus,  147. 

dentatus,  147. 

gracilis,  147. 

lenticularis,  162. 

Nuclei,  Inner,  of  retina,  311. 

,  Outer,  of  retina,  312. 

Nymphse,  270. 

Odontoblasts,  173,  174,  177. 
(Esopbagus,  19 1. 
Oil-globule,  39,  40. 
Olfactory  cells,  336. 

nerves,  111,  159. 

Olivary  bodies,  143. 

nucleus,  147. 

Omentum  of  cat,  29. 

of  frog,  89. 

of  guinea-pig,  40. 

of  rat,  32. 

,  Structure  of,  33. 

Optic  nerve,  317. 

nerve-fibres,  310. 

tract,  162. 

vesicle,  316. 

Ora  serrata,  310. 

Organ  of  Corti,  328,  329,  332. 

of  Giralde,  251. 

of  Jacobson,  337,  338. 

Ossein,  52. 

Osseous  labyrinth  of  ear,  321. 

lamellae,  52. 

— —  substance  from   osteoblasts, 

61. 
Ossicula  auditus,  319. 
Ossifying  cartilage,  48. 
Osteoblasts  forming  bone,  50,  57, 

61. 
Osteoclasts,  62. 
Osteogenetic  layer,  49. 
Otoliths,  324. 
Oval  nucleus,  39. 
Ovary,  65,  257. 

,  Development  of,  263. 

,  Lymphatics  of,  268. 

,  Nerves  of,  268. 

Oviduct,  65,  265. 
Ovum,  1,  259. 

Pacinian  corpuscles,  115,  121,  291. 

Palate,  187. 

Palmae  plicatse,  266. 

Palpebrae,  293. 

Pancreas,  208,  209. 

Papilla  circumvallata,  192.   • 

filiformis,  191. 

foliata,  193. 

fungiformis,  191. 

nervi  optici,  303. 


350 


Elements  of  Histology. 


Papillary  hair  of  Unna,  280. 

muscle,  75. 

Paraglobulin,  12. 

Parenchyma  of  testis,  253. 

Parenchymatous  cartilage,  48. 

Parietal  cells,  199. 

Pars  ciliaris  retinas,  303,  305,  310. 

membranacea,  254. 

prostatica,  254. 

Pedunculated    hydatid    of    Mor- 
gagni,  251. 

Pedunculus  cerebelli,  144,  152. 

Penis,  255. 

corpora  cavernosa,  255. 

nerve  endings,  120. 

Peptic  glands,  197. 

Peribronchial  lymphatics,  220, 224. 

Pericardial  cavities,  88. 

Pericellular  space,  141. 

Perichondrium,  45,  46. 

Perilymph,  321. 

Perimysium,  66. 

Perineurium,  104,  121. 

Periosteal  bone,  59,  61. 

formation,  55. 

processes  of  Virchow,  55. 

Periosteum,  50. 

Peripheral  nerve- endings,  112, 115. 

Peritoneal  cavities,  88. 

Peritoneum,  65. 

Perivascular  lymphatics,  89,  224. 

lymph-spaces,  151. 

spaces  of  His,  141. 

Pes,  161. 

Peyer's  glands,  95,  205. 

patch,  95. 

Pharynx,  190. 

tonsil,  94,  190. 

Pia  mater,  80,  127. 
Pial  sheath,  317. 
Pigment  cells,  23,  37. 
Plasma,  10. 

cells,  41,  100. 

Pleura  pulmonalis,  65,  220. 
Pleural  cavities,  88. 
Plexus  choroideus,  150. 

myentericus,  173,  201,  217. 

of  Meissner,  201,  207. 

venosus  vaginalis,  269. 

Plicae  villosse,  197,  204. 
Pons  Varolii,  142,  152,  154,  159. 
Porta  hepatis,  210. 
Portio  Mulleri,  3C0. 

vaginalis  uteri,  266. 

Posterior  nerve  roots  from  spiral 

cord,  136. 
Prickle  cells,  23. 
Primitive  dental  groove,  175. 
fibrillte,  107,  111,  138. 


Primitive  fibrils,  69,  113. 

ora,  263. 

Prostate,  253. 
Protoplasm,  1. 

,  Structure  of,  6. 

Protoplasmic  membrane,  39. 
Proximal  convoluted  tubule,  235. 
Pulp  tissue,  227. 
Pulvinar,  162. 

Purkinje's  ganglion  cells,  152,  154. 
Pyloric  glands,  196,  199. 
Pyramid  of  Ferrein,  233. 
Pyramidal  decussation,  142. 
tracts,  142. 

Rami  capsulares,  214. 
Ranvier's  constrictions,  108. 

nodes,  108. 

Raphe,  147, 156. 
Red  blood  corpuscles,  10,  12. 
Reissner's  membrane,  326,  328. 
Remak's  fibrous  layer,  77. 

nerve-fibre,  111. 

Rete  Malpighii,  19. 

mucosum,  19. 

testis,  250. 

Reticular  cartilage,  49. 

formation,  156. 

Retina,  308. 

,  Blind  spot  of,  309. 

,  Blood-vessels  of,  317. 

,  Ganglion  cells  of,  311. 

,  Lymphatics  of,  317. 

Rhodopsin  of  Kuhne,  314. 
Rods  and  cones,  313. 
Rollet's  secondary  substance,  68. 
Rosette  stage  in  nucleus,  8. 
Rugae,  268. 

Saccules,  321,  322. 

Saccus  endolymphaticus,  321. 

Saliva,  189. 

Salivary  cells,  182. 

glands,  178. 

,  Blood-vessels  of,  186. 

,  Ducts  of,  180. 

,  Lobes  of,  180. 

,  Lobules  of,  180. 

,  Lymphatics  of,  186. 

,  Nerves  of,  186. 

Sarcode  of  Dujardin,  5. 
Sarcolemma,  6*7,  68,  72. 
Scala  tympani,  320. 

vestibuli,  320. 

Schultze's  protoplasm,  5. 
Schwann's  cells,  5. 
Sclerotic,  298. 
Scrotum,  64. 
Sebaceous  follicles,  286. 


Index. 


35* 


Semicircular  canals,  320,  322. 
Semilunar  valves,  75,  86. 
Seminal  cells,  247. 

tubules,  246,  252. 

Sensory  ganglion  cells,  141. 
Septum  cisternse  lyinphaticae,  30. 
Serous  glands,  178,  188. 

membranes,  89. 

Sesamoid  cartilages,  48. 
Sharpey's  perforating  fibres,  54. 
Sheath  of  Henle,  116,  119. 

of  Schwann,  108. 

Simple  axis  cylinders,  111,  114. 

lymphatic  glands,  92. 

Skin,  274. 

blood-vessels  of,  289. 

lymphatics  of,  290. 

nerves  of,  290. 

Solitary  glands,  95. 

lymph  follicles,  205. 

Spaces  01  Fontana,  299. 
Spermatoblasts,  247. 
Spermatozoa,  249. 
Sphincter  papillae,  301. 
Sphincters,  65. 
Spinal  cord,  127. 

grey  matter,  128,  136.      ' 

white  matter,  128,  130. 

Spiral  tubule,  237. 
Spleen,  225. 

,  Capsule  of,  225. 

,  Lymphatics  of,  229. 

,  Nerve-fibres  of,  229. 

,  Parenchyma  of,  226. 

,  Pulp  of,  226. 

,  Red  blood  corpuscles  of,  16. 

,  Trabecule  of,  226. 

Spongy  bone  substance,  54. 
Squamous  epithelial  cells,  18. 
Sternal  cartilage,  47. 
Stigmata,  82. 
Stomach,  196. 
Stomata,  29,  82,  89,  224. 
Stratified   columnar    epithelium, 

21. 

pavement  epithelium,  20. 

Stratum  adiposum,  276. 

cinereum,  160. 

corneum,  19,  274. 

■ gelatinosum,  159. 

gloinerulosum,  159. 

lucidum,  19. 

Malpighii,  274. 

opticum,  160. 

Stria  vascularis,  328. 

Stroma,  12. 

Subarachnoidal    spaces,    88,    127, 

150,  318. 
tissue,  128. 


Subcutaneous  lymphatics,  88. 
Subcutaneous  tissue,  275. 
Subdural  spaces,  88,  127,  150. 
Subendocardial  tissue,  74,  75. 
Subepithelial  endothelium  of  De- 

bove,  35. 
Subhyaloid  cells,  307. 
Submaxillary  ganglion,  163. 
Submucosa,  189. 
Submucous  lymphatics,  88. 
Subpericardial    nerve    branches, 

76. 

tissue,  74. 

Substantia  gelatinosa,  13  i. 

nigra,  161. 

Subvaginal  space,  318. 
Sudoriferous  canal,  276,  277. 
Sulcus  hippocampi,  159. 

spiralis,  327,  328. 

Superior     pedunculus     cerebelli, 

162. 
Suprachoroidal  tissue,  300. 
Suprarenal  bodies,  340. 
Supravaginal  space,  318. 
Sweat  glands,  65,  276,  290. 
Sympathetic  system,  166. 
Synovial  cavities,  88. 

Tactile  corpuscles,  115,  118. 

hairs,  286. 

Tapetum    nigrum,  301,   303,   305, 

315. 
Tarsal  plate,  292,  293. 
Taste  buds,  193. 

cells,  193. 

goblets,  193. 

Teeth,  171. 

cement,  174. 

development,  175. 

pulp,  174. 

Tegmental  ceds,  193. 
Tegmentum,  160,  161. 
Teichmann's  crystals,  13. 
Tendon  cells,  33. 
Tendons,  87. 
Tenonian  capsule,  318. 

space,  318. 

Tensor  choroidese,  300. 
Terminal  bronchi,  221. 
Testis,  244. 

Thalamencephalon,  161. 
Thalamus  opticus,  157,  161,  162. 
Thoracic  duct,  84. 
Thymus  follicles,  96. 

gland,  96. 

Thyroid  cartilage,  46. 

gland,  339,  340. 

Tongue,  190. 

serous  glands  of,  191. 


352 


Elements  of  Histology. 


Tonsils,  95. 

Touch-cells  of  Merkel,  115,  119. 

corpuscles'  of  Mtrkel,  120. 

Trabecules  carnese,  75. 

of  lymphatics,  65. 

of  spleen,  65. 

Trachea,  46,  65,  217. 
Tractus  olfactorius,  159. 

opticus,  162. 

Transitional  epithelium,  21. 
Tuba  Eustaclui,  319. 
Tuber  cinereum,  161,  163. 
Tubercle  of  Eolando,  145. 
Tubes  of  epididymis,  252. 
Tunica  adnata,  244. 

albuginea,  244. 

dartos,  65. 

fibrosa,  261. 

propria,  328. 

vaginalis,  244. 

Tyson's  glands,  255. 

Urea,  301. 
Ureter,  230,  243. 
Urethra,  Female,  269. 

,  Male,  254. 

Urinary  tubules,  231. 
Uterus,  64,  265. 
Utricle,  321. 

Vagina,  65,  268. 
Varicose  nerve-fibres,  110. 
Vas  deferens,  65,  252. 

rectum,  250. 

Vasa  efferentia,  250. 
Vascularisation  of  cartilage,  55. 
Vater's  corpuscles,  115. 
Veins,  65. 

,  Intima  of,  79. 

,  Media  of,  79. 

of  the  bones,  78. 


Veins  of  the  brain,  cord,  gravid 
uterus,  membranes,  and  retita, 
80. 

,  Valves  of,  79. 

Vena  axillaris,  azygos,  cava,  cru- 
ralis,  hepatica,  intima,  iliaca, 
mesenterica,  poplitea,  renahp, 
spermatica,  and  umbiHcalis,  80. 

jugularis,  and  subclavia,  79. 

Venae  rectse,  242. 

stellatse,  242. 

vorticosaB,  305. 

Venous  radicles,  227. 

sinuses,  227. 

Ventricle,  Fourth,  148. 

Ventricles,  76. 

Vesicula?,  seminales,  65,  252. 

Vestibulum,  270. 

Virchow's  crystals,  13. 

Visceral  pericardium,  74, 

peritoneum,  194. 

Vitreous  body,  307. 

White  blood  corpuscles,  13,  16. 

commissure,  135. 

fibrous  tissue,  30,  31. 

substance  of  brain,  151. 

of  cord,  110. 

of  Schwann,  107,  108. 

Wolffian  body,  258. 

Wreath  arrangement  of  nucleus,  8. 

Yellow  elastic  cartilage,  49. 
tissue,  43. 

Zona  fasciculata,  341. 

glomerulosa  r  340. 

pellucida,  259. 

reticularis,  341. 

vasculosa,  257. 

Zonula  ciliaris,  307. 


UAfcbELL,  PiTTEH,  GAUUK   &   CO.,  BELLK  SADVACiE  WOHKS,    LONDON',  E.G. 


WM651 


K  1  #a  -i  ri 


K672 


